whattup everyone Im in need of some help badly.. I have a 1987 Monte Carlo luxury sport all stock with the 305...
here's the problem
car runs and shifts perfectly till about 15-20 mins of driving then it won't downshift...when coming to a stop it almost dies out then goes into first gear.. then when accelerating it up shifts early.. I can manually **** it but even then sometimes it shifts hard.. the engine light came on and it was saying the tps sensor was bad so I had it changed and that's pretty much when all the problems started... kickdown cable and everything else looks perfect... need help PLEASE... my car has only a lil over 45,000 miles and I wouldn't expect to have transmission problems this soon... I baby my car and barely even drive it.. hope it's not something major... please help!!! Hope to hear from u guys soon... thanks

 

Could be the modulator valve, or vacuum hose rotten going to it. That will affect the shifting except when you get on it, and not downshifting is the cable or adjustment.

 

Thanks for the reply... where is the modulator valve located?

 

It will be on the transmission with a vacuum hose attached (or should be)

 

Ok just looked and the transmission is a "turbo hydramatic"... don't see any modulator or vacuum hose going to it... unless it's in a hard to see spot?? Help needed please!!! Thanks

 

I'd suggest looking online for a schematic or get a chassis service manual for your car. 1987 isn't old, but it does have vacumm actuated devices such as a transmission shift modulator valve, even my 96 still uses old , but reliable technology.
I'd add the modulator valve possibly will be at the rear of the transmission, you might google it to find what it looks like