Alright, I've got a '91 Z/28, 305 TPI, 700r4. When the car is cold, transmission shifts perfectly, not a blip, slip or rattle to be had. As soon as the car heats up and gets to running temperature, man if the damn thing won't shift into 4th gear.

Fresh fluid/filter, properly adjusted TV cable, I'm pretty lost. It will shift into 4th eventually, but I have to be giving it enough gas that the car is accelerating, which isn't exactly a good idea on the highway...as soon as I hit a steady speed, it drops back down into 3rd.

Is it possible that the 4th gear band/valve is just worn out so much that it's not catching? I tried putting some of that lucas transmission fix crap in, but that did nothing, I didn't really expect it to, honestly, but I had some lying around.

Fluid level is about 3/4 of the way up on the full scoring area on the dipstick when hot.

Best part is, I'm leaving on a 200 mile trip tomorrow (moving) and I have to drive the car there. Conveniently, every time I make this trip (to school) I have some problem with my car. It has never failed, I've owned 3 3rd gens, and every single one of them had a problem the night before I made the trip, without fail. From alternators to starters to sensors, I think god must be giving me a sign.

 

I would suspect a TV issue with the throttle valve getting stuck perhaps

 

I had a huge hunch that it was a TV thing, not sure why, so I went out and checked it again, sure enough, the detent was cracked, causing too much slack in the TV cable.

Funny thing is, I adjusted it last week and the detent looked perfectly fine...

 

doh

 

Yea..that was a real face-palm moment.