The best bet on that is to go to a GM dealer and pick up a 4oz bottle of "friction limiter", put it in your transmission...works every time
My transmission shifts into all gears but in drive it shifts into high gear at 60 MPH and 5000 rpm and downshifts at 45 MPH. Already changed filter kit and modulator valve and flushed transmission with fluid changed. Why am I still having this problem
Well there are a cupple things. 1 make sure you have vacc. To your modulator. 2. Check to see if your kick down cable is not stuck. Or 3. There is a broken valvebody spring. All of witch you should beable to fix without pulling the tanny.