My 1997 Tahoe just started with a new problem.
When its cold, the speedometer jumps around like crazy.
At the same time, the transmission is shifting like mad, several times a second. Like it doesn't know which gear it wants to shift into. Then, to make it even more interesting, the anti-lock brakes engage - presumably because it can't accurately read the speed.

Once it warms up it is fine (so far).

Took it to a shop and of course they couldn't duplicate the problem. And to my surprise they said it is probably NOT the speed sensor. So...

Anyone have any suggestions?
P.S. there are no trouble codes.

 

Well, the speedometer cable is wired into the transmission and with the transmission acting weird i think it's time for a trip to the transmission guys. Check your fluid level first though.

I think the anti-lock brakes are unrelated and most likely corrosion on a wheel sensor. Very common on 97, I know, I own one. Pull the wheels and clean up the sensors and that should rectify that problem.