700R4, Automatic transmission. I recently replaced my ECM on my 1989 RS, to combat problems that I was having with the transmission shifting oddly. When starting up and running cold, it shifts fine. However, once the car is warmed up to around 120-140 degrees, things get temperamental. The transmission is shifting WAY too early, shifting into 4th at around 15mph. As stated, this does not happen when it's cold, or when the car is warming up. I'm guessing that something temperature related is telling my transmission bad things. Could it be the coolant temperature sensor? What else could be my problem? It also tries to kill it when coming to a stop once warmed up, but not when cold. I'm just at my end with this car... Due to previous thread misreads, I'm going to state it again. I only have problems with the transmission once the car is warmed up completely. Not when it's cold. Also, it takes around 5 seconds to shift into OD and D. However, it shifts right away into 1 or 2, and R. Could this be part of my problem?

Personally I do not think that the ECM has anything to do with it because it does not control the shift points, only when the TC locks up, the newer 4l60e is controlled by the PCM. I would drop the pan and flush the tranny, put fresh oil and a filter if it has not been done in a while. Check the TV cable to make sure that it is adjusted properly. The only other thing is to bring it to a tranny shop.

Thanks for the info...

But I think I'm just going to sell off the car. I'm tired of having to deal with all this crap that it's giving me.