Intermittent speedometer problem

[guy3310]

I have a 99 Tahoe police package 2WD and at times the speedometer will begin to jump wildly starting around 50-60 MPH. Below that speed, it is usually rock steady and seems accurate. Also, when it is jumping (10-20 MPH jumps!) the transmission feels as though it is shifting in/out of OD, or maybe the torque converter is locking/unlocking? When this "shift" occurs, the tach jumps up slightly. All the other gauges work great. When the speedometer acts up, it will kick the cruise control off too. This is an intermittent problem, doesn't happen all the time. Can anyone help?? Thanks.

 

[79powerwagon]

Is your check engine light on?

 

[guy3310]

No, the check engine light has not come on at all. The other night, for the first time with this problem, the anti-lock brake light came on and stayed on. The next day, after being parked overnight, this light was not on anymore.

 

[Untitled415]

If the car still shifts ok when this happens the problem will most likely but in the dash if not check your speedo and wiring

 

[guy3310]

Appreciate the input. When this problem has occurred before, I noticed the headlights would flicker occasionally as though there is a bad connection or something. Someone told me to check the alternator out, that's my next step I think.