hesitation/bucking in my 99 Tahoe

I have a 99 Tahoe that I purchased in May. Right from the start it had an issue with intermittent bucking, mostly under the following conditions - after upshift from 3 to 4 especially under load, at highway speeds when letting off the throttle and then trying to resume acceleration, and sporadically while driving at steady speeds.
I've had several mechanics look at the vehicle, I have replaced the fuel filter, distributor(with an all metal NEW distributor, not a reman.) and had the transmission completely rebuilt. The symptom still persists. The truck is drivable, but the issue is making me insane. It's been suggested that there could be slack in the timing chain, possibly an issue with an injector, maybe an electrical issue with the ignition, but nothing shows on the computer.
The engine was replaced before I bought the truck, and it runs perfectly with the exception of the bucking issue. Idle is perfect, acceleration good, everything seems right.
The vehicle does have a remote starter, and I have wondered if that could be related to the problem.
Any help would be appreciated.

TCC lockup in the valve body is worn I bet....

The transmission was completely rebuilt by a very reputable shop, including torque converter and electronics - wouldn't the TCC lockup & valve body be part of that job?

I vote torque converter

It seems like that to me too, but as I said the tranny has been completely rebuilt including torque converter. I was just out driving the truck again and create the symptom at will - if I accelerate hard as soon as I let up on the pedal the truck lurches violently.

Had the same problem/symptoms years ago on a S-10. Tranny was pulled/overhauled 3 times, including replacing burnt torque converter, by a very exasporated/frustrated tranny shop. Finally fixed, they claimed, by fixing a bad ground. Tranny shops goof-up, too...

Tex99 - can you elaborate on your symptoms and the fix? I'm so done with this problem. I love the truck, looked around for months before I found what I thought was the right replacement for my 95 Tahoe, but I'm now stuck with this 99 that I have $7k into and for all practical purposes it is un-driveable. Ready to put my head in a noose...

Wow, there's so much to say about that incident it would fill a book, so I'll cut to the chase.

My tranny oil had turned brownish, smelled burnt, caused by the constant lock/unlock of the lockup torque converter that happens when on cruise control in hilly terrain. Tranny shop talked me into overhaul and heavy-duty torque converter (thicker steel section).

After the overhaul, with rebuilt heavy-duty torque converter, it would demonstrate your symptoms within just a few miles from the shop. I would limp back, the shop owner would pull the dipstick and go through gyrations claiming the tranny oil was too hot (which it wasn't, but having been a mechanic I knew about these avoidance tricks). I would simply say: "So you think that's the problem, and can you fix it?"

Completely defuses the confrontation, and lets him think he's in full control, while I look at him like a child with a broken toy.

He put it back in the shop, did another overhaul, replaced the torque converter. Had to, just that short stint ruined the overhaul and burnt the torque converter.

They test drove it, worked fine, then I took it home, only to have it act up again several miles later. Limped back, and we went thru this all over again.

Now, this happened 3 times in a row. Takes a lot of patience to endure this, but often half of auto maintenance is a good working relationship with shops, very important, as mechanical maladies are just as stressful on the shop. Rather than being a confrontation issue, the shop now took this on as a "We're gonna solve this, by golly!"

The point here is that your overhaul is probably shot, gotta do it again...

So - back to the tranny shop this morning. Drove the truck with the guy I've been working with and confirmed that the symptoms are in fact the TCC coming in and out of lockup. Went over the build with him again - everything replaced including valve body and TCC solenoid. We hooked the truck up to the scanner even though no CEL and actually retrieved 2 codes - p0340 which is an ignition misfire code and p1345 which is camshaft to crankshaft correlation sensor error code. Can't pinpoint exact cause, he wants me to drive the truck and hope it gets worse so the problem is easier to nail down.

Is your tranny oil turning brownish or smelling burnt yet?

Nice to have the TCC issue confirmed, not sure about the solution.

There are many things, simple things, that can go wrong that aren't picked-up by a diagnostic scan, like intermittant/aged/poor grounds. Another member here had bought a truck with a rebuilt engine. He took a pic of a mysterious dangling braided cable. Turns out, the engine/frame grounding cable(s) were simply cut to get the engine out, then never reconnected or replaced.

There's also conditions that have to be met before the TCC is allowed to enter lockup, like proper coolant temperature and computer in closed-loop mode, plus others. Possibly something intermittant here, perhaps from gorilla-handling parts of the wiring during engine removal.

My cousin's older car would demonstrate TCC issues, tracked down to a faulty section of the ECC. The driver transistor, which sends a lot of current to to energize the solenoid, had failed due to heat/age and water incursion. It created many non-sensical symptoms, and it was like pulling teeth trying to get him to understand this cause. He still doesn't get it, and continues to periodically disconnect the battery (to reset the computer) even though it's not necessary now.

With your engine/trans jumping/jerking/bucking from a in/out TCC, I'm not surprised you're getting a crank/cam timing disconnect.

Bottom line: I'm thinking something intermittant in the electrical. The TCC solenoid needs a healthy power source and a good/solid ground. Could start looking there...

Appreciate all of your input. So far the fluid is still nice - red and no burnt smell. I do feel like my tranny guy is doing everything he can to help track this down. They are the ones who put the new dist. in, even though I had already had a remanufactured one put in by a mechanic at the shop where I initially took the truck for diagnostics.He has reassured me that when we are able to determine the exact cause he'll work with me to get it straightened out. Problem is, right now we don't know what's causing it to do what it's doing. His approach, as I said earlier, is rather than start spending money randomly, drive it some and hope that the problem presents in a more substantial way. My main concern is that never happens.........
Unfortunately I have neither the knowledge/experience/time or the $$$ to pay someone else at this point to whack away at this trying to figure it out. I guess I'm stuck putting some miles on and taking a wait and see approach for now.
We cleared the codes and my guy said drive it for a week or so, then lets hook it back up and see what we get -
What else can I do?
BTW - I don't think there's any question that things were "gorilla handled" - when they pulled the tranny they found some wiring that was cobbled from the engine swap, grounds that were hanging, etc. and fixed what they found. The reason that the dist. got changed originally was because the tabs had been broken off and wood screws were used to hold the cap on. I bought the truck from a guy who works for a GM dealership and it was represented that the engine swap was done by a GM Master Tech - everyone who's touched the truck agrees - BS, F'in BS. In spite of that, we have the truck running beautifully - aside from the TCC issue.....

Good to hear the oil's fine. I guess something else you could do is drive it in "3" instead of "Drive". If it doesn't buck/jump then that's good diag info, plus you won't damage your truck. Some trucks also have an "OD on/off" switch (overdrive on/off). If you have this, could try turning it off.

While driving in "3", you could shift it to "Drive" only after hitting highway speed, what it does then can help diag this thing, and if it upshifts fine then, again, you're not breaking things.

Good confirming the electrical nightmare, sounds like this may still be the focal point...

Tried the driving in "3" thing, just as a "diagnostic" check yesterday. It will exhibit the same symptoms whether it's in "3" or Drive, also throughout different speed ranges. It does seem less prominent, even non-existent at times if I drive the truck very easy - it also seems more prevalent once the truck is warmed up. Like you, I'm leaning towards an electrical issue.

OK - I am getting discouraged. The more I search these codes and the possible causes the more I view them as the death knell for my truck, it seems unlikely at best that I will ever trace this problem down. I am stuck with a truck that looks great but will never run right, anyone interested? I'm close to an auction sale...

Hang in there, Stripermike, got a coupla more things to try. The data you got while driving in "3" is significant. Doesn't give us an immediate answer, but the tranny guys need to know this. You're collecting diagnostic clues that are parts of an overall picture. Don't expect to try to figure this out yourself, it won't make sense.

Next, do some driving in "2", then "1", then (if you're comfortable doing this) in "R"everse. Keep good notes on what it's doing in each gear range.

Then, if it's acting up in a particular gear, immediately select some other gear and note any changes. Include shifting to "N"eutral in these tests.

Of course, don't push it so the truck gets hurt. Do these tests with the engine fully warmed up.

The final problem could something complicated in the computer or valve body, or could be a simple broken wire. These tests are free, don't cost you anything. Unless you're really exasperated, I think it's worth it to know for sure. Hate to see you toss it out if it's a simple problem.

Speaking of free, AAmco offers free driving diagnostic, no commitment, could really help...

Been driving it every day - one thing I seem to be noticing is that it doesn't act up during acceleration. Most often the problems occur when I let up on the gas after accelerating or right after an upshift, when the rpm's drop. To me this seems to indicate that for one reason or another there is a voltage drop to the TCC solenoid when the rpm's drop. Any thoughts on whether this could be an ignition coil problem? Is there a way I can test the coil?

Good, good, you're producing diagnostic info. Again, don't try to solve this yourself, there are so many other things going on in there, they're all part of this puzzle. With the symptoms occurring independantly of gear selection, but more closely associated with throttle input following loading, the focus now shifts to the engine sensors and management.

A lot of things are changing in your scenario, like throttle position sensor, manifold air pressure, engine torque, engine rpm, ignition timing, vehicle speed, just to name a few. All these, plus more, are feeding into the engine/vehicle control computers, and they're making changes to accomodate this new input. Normal maladies are noted and stored, abnormal maladies cause abnormal symptoms, and can cause other, irrevelant codes to be stored, leading folks off in the wrong direction.

The next 'free' trick you could try is to refreshen all the electrical connections. Get a can (or 2) of electronics cleaner, disconnect the battery ground (very important), and methododically disconnect/clean/reconnect every sensor and computer connector you can possibly find in there. Age alone justifies this.

Then reconnect the battery negative ground, and resume your driving diagnostics, repeating what you've done before, and noting any differences.

Would be great if the symptoms disappear, but that would be rare. If no changes, then the connectors and associated wiring are probably ok. Sometimes, just the act of manipulating the wiring can change things, indicating a bad wire somewhere.

I have a ScanGuage II mounted on my dash, very handy, inexpensive, reveals important info during driving. It could reveal something as simple as a temperature sensor putting out wrong temperature, but not wrong enuff to trigger an OBD code, but wrong enuff to cause the engine control computer to make wrong choices, like whether or not to engage TCC.

Hopefully you've now got a better picture of the diagnostics game, it's not always single symptom leads to single solution. More like a chess game, or, one of my favorites, 'mastermind', requiring sherlock holmes type logic to weed thru all the noise.

You're doing fine, keep up the meticulous notes, and at the appropriate time, present them, and this forum thread, to your mechanic, he'll appreciate it...

Another free thing, pull the distributor cap and try to push down lightly and turn clockwise/counter clockwise, see how much slop there is in the gears.....

Haven't had much time to do any real diagnostics this week, besides the normal act of driving. Have to say, the more I drove this truck the more disgusted I get.
Having driven a 95 with the same exact engine and drive train as this truck I have a feel for how things should be. This truck ain't it. While the engine runs smooth, much smoother in fact than the 95 ever did, and the power on acceleration is great, the truck has major drive train issues, even with a completely "new" transmission, and a ton of extra time spent by mechanics looking at the rear diff, transfer case, etc.
Now, after driving it 400 or 500 miles this week, there are other symptoms coming to the surface. When taking off from a stop there is a loud "clunk". Sometimes there are actually 2 loud "clunks". My initial reaction was U-joint. Crawled under the truck to check it out and - front joints were replaced when the tranny got done done, rears seem fine. No slop in the driveshaft with truck in neutral.
The only way I can describe the sound, which seems to be getting worse, is that it sounds like a metal shaft sliding backwards until it bottoms out on another metal part. When you are driving the truck it feels like this is happening somewhere up front - motor/tranny area - but I know that could be misleading.
As I said, the more I drive this truck the more I feel like things will never be right with it. Anyone looking for a real sharp overpriced 99 Tahoe as a project truck?!?#@$%!&^?

Did I mention that the TCC lockup condition, whatever it's being caused by, seems to be getting worse? At one point this afternoon while driving my daughter to a friend's house the truck "lurched" violently 3 or 4 times in about a mile of back road driving.