Hey Scotty, have a 2002 pontiac grand prix that does not go into 4th gear. It also shifts erratically sometimes. I know that the engine and transmission in the car are not the original, but I believe the Computer is still programmed to the supercharged engine it used to have. Any ideas?

yea, dont buy one of those clunkers in the first place. Trannies stink big time. But, find a guy like me to road test it with his scan tool hooked up and pray it's a bad shift solenoid or valve body