05 hoe, transmission slipping

[mkatts]

have a new to me 05 tahoe. When I punch it at 50+ mph, it kicks down into 2nd gear and the rpms shoot up to 5-6 grand!
At this point I am not sure if it's slipping or if it's actually kicking down to 2nd gear. If I just ease into it, it works fine, but no matter what speed I am at, if I put it to the floor it kicks way down and the rpms' readline!
Anyone heard of this?
What can I expect if I take it to a trans shop?

 

[Rivieraracing]

Sounds like it is doing what it is suppose to do, kicking the trans into the lower gears for passing power, sounds good to me!!

 

[mkatts]

I don't think it should be kicking down so hard that I readline the RPM's. I have owned Chevy's my whole life. Traded in a 03 Avalanche for this one and it did not act like this.

 

[Rivieraracing]

I don't know what to tell you, I have a denali with a 6.0 and if I mash the pedal it will go all the way to second, practically redline, and then off I go. Those tranny's are going to go as low as they feel like they need too without going too low at high speeds, that way you have passing power. I'm sure others will chime in if I am wrong but mine does the same as yours does, but for me that is a good thing!!

 

[mkatts]

You run all the way up to 6000 RPM all the time with no problems?

 

[Rivieraracing]

I don't run it all the time at 6k, all I am saying is when I really need to step on it it does the same thing that yours is doing, if you don't want to go that low with the tranny then you can't mash the pedal, but the option is always there!!

 

[mkatts]

nah, I still think we are talking different here. I took it out last night and from 30 mph, I put it to the floor, the rpms went up a little, then it down shifted and shot to 6000 and stayed there up to 70 mph. There is no way that is right. It's let off until I did. No commercial production chevy engine is designed to run up to 6000 and stay there. I can see if for a quick burst, but I should not be in 2nd gear at 70mph. Ever. I more so think you are either mistaken about what gear you are going into or there is something wrong with yours and you don't realize it.
I went to the dealer and test drove another 05 last night. It did not react as mine does. From 30 mph cruising, I punched it down, it down shifted to 3rd, went up to about 4500 rpm and shifted back to 4th once I hit 70mph.
thanks anyway for your input.

 

[diehrd]

My 02 tahoe does that as well , BUT I have a tuned PCM.

Slipping would mean the tranny is not outputting power , the internals are not connected solid to a gear and the engine revs and no power flows to the rear wheels. What you are stating is not slippage.

 

[41racing]

There is no way your tach can read 6000 rpm's from 30 all the way up to 70. It would have to change rpm or the truck wouldn't accelerate. Maybe something is wrong with your tach. I suppose that it could possibly be reading high. A buddy of mine has a 02 2500HD gmc with the 6.0, and when we pulled his enclosed trailor it would do what your truck is doing. But it would only pull to 5000, and it would do that a lot.

 

[mkatts]

ok, mistyped it. I was running 6000 rpm at 70 and climbing. It will not shift up to 3rd or 4th. I don't care if I have it to the floor or not, the ECM should not allow it to be in 2nd gear at 6000 rpm. It should up shift to 3rd at the very least. The tach is not reading wrong. I can tell what that the engine is running high rpms by sound. There is a bit of a difference between 1500-2000 cruisung and screaming at 6000.
Either I am not explaining myself well enough (most likely) or what I am experiening is something no one else here has ever encounterd. I have been working on chevys for 20+ years and have never had one act like this except a slipping transmission. This seems like it kicks down to 2nd and stays there until I let off the pedal.

 

[diehrd]

If u worked on any autos for 20 years you would know what a transmission slip is , what you are describing IS NOT A SLIP............. It is a delayed up shift , And I would bet at sometime in that trrucks life some owner reprogrammed the PCM which almost always alters shift points , deletes some TM and removes the governor , and will allow the truck to spin usually to a max of 6100 rpm..

Slipping at 6k would mean the truck is NOT MOVING FORWARD, OR it is not pulling any longer you clearly state it is hitting 70mph , a slipping tranny is incapable of hitting 70mph in any gear that is slipping.

 

[azfitch]

mkatts,
I know exactly what you are talking about. I have a new to me 05 tahoe with 90k on it. I notice your problem the most when cruise control is engaged. Ill be cruising up a small slope and the tranny down shifts, then all of a sudden it drops into 2nd gear at 70 mph. I thought something was wrong with mine too, but I guess I just got use to it. My impression of the situation is that my tranny never gives 3rd gear a chance and drops into 2nd way too often at 6000 rpm @70+ mph. Let me know what ever happens with your problem, as mine sounds exactly the same.

 

[mkatts]

If u worked on any autos for 20 years you would know what a transmission slip is , what you are describing IS NOT A SLIP............. It is a delayed up shift , And I would bet at sometime in that trrucks life some owner reprogrammed the PCM which almost always alters shift points , deletes some TM and removes the governor , and will allow the truck to spin usually to a max of 6100 rpm..

Slipping at 6k would mean the truck is NOT MOVING FORWARD, OR it is not pulling any longer you clearly state it is hitting 70mph , a slipping tranny is incapable of hitting 70mph in any gear that is slipping.

For the love of god, I already said I mistyped above. I do not think it's slipping. I think it is shifting down to 2nd gear when I don't think it should. @ 70 mph I should not ever be in 2nd gear.
so drop the slipping idea.

azfitch,
Thanks for validating that I am not alone.

So how can tell if someone messed with the pcm and how can I fix it?

 

[sasquatch094]

my 03 silverado does 70 in second gear.. soo idk.. i cant tell u the exact rpms on it, but at that man my silverado is going nuts, jumping and ****.. anyones 6.0 fog the street up in the cold mornings? haha when i punch it man smoke (fog,or idk steam whatever u wanna call it) pours out of the exhaust and u cant see **** behind u.. hahah

 

[Rivieraracing]

I tell you what, tomorrow I will probably head over to my parents place on some back roads and I will put my Yukon to the test. I'll mash the pedal and see what mine does, see if it is the same as what yours does! I will let you know what I come up with after I experiement a little.

 

[Rivieraracing]

I also agree azfitch, mine will do the same if it has to while it is on cruise control as well, my tranny has been pretty good at deciding what gear to be in when it needs too (just sometimes it is more noticeable than others ).

 

[Rivieraracing]

Ok, just to let you know I tested out my yukon today to see what mine did when I mashed the pedal down while driving 50mph and whether it was in drive or in 3rd, it rocketed into second all the way up to 5k at 75mph exactly everytime, no matter what I did, even in tow/haul mode. The only way it would probably go above that while in second is if I was pulling my toyhauler (I think I have seen it all the way up to about 5500rpm while climbing a hill before it would upshift) or if I manually put it into second gear (I wasn't about to do that, I'm pretty sure what would have been the result of that!!). Also for comparison for you, mine at 3k and 4k and at 5k, it ran 45mph and 60mph and at 75mph respectively, and I think mine should have came with 3.73 gearing stock (not sure if it still is but that was what I ran today). I am starting to agree with the other guy about the fact that your computer may have a sort of custom tune of some sort and that the shift points that are controlled by the computer my have been changed. Heck, maybe your gearing has been changed before you bought the truck and that the shift points haven't been changed to accomodate the new gearing, just an idea!! Also for comparison, my tach only goes up to 6k without a visible "redline", is yours the same? Hope this all helps out and isn't too confusing, and if there is anything else you want me to check out on mine for comparison, let me know!!

 

[mkatts]

Thanks for the experimenting and the time you spent doing it.
Is there any way to tell if the shift points have been messed with? I assume I need to find someone with a programmer or buy my own, but never having seen one of these programmers, I guess I need to do some research on them.

 

[Rivieraracing]

I am not sure if and how you can find out if some programming has been done other than picking other peoples brains and their trucks and getting some more comparisons of how their rigs react. Other than that, I hate to say it but the stealership should be able to help, sometimes they are pretty helpful but usually for a little (or big) $$$$. But until then, just do some more research on here and pick some more brains, you never know!!!

 

[mkatts]

Took it out last night. Was going onto an on ramp at 40mph. Punched it, it kicked down to 2nd and stayed there up to 80mph when the tach hit 6000 and the engied started to cut out. I assume it has a rev-limiter. I let off and shifted back up to 3rd then 4th right away. Think I will take it to the deal to have the compter read and see if anything is out of spec.

Thanks again.