Transmission compatibility

Your transaxle is a 4T65E and they come on many FWD GM vehicles. Some will have different final drive gear ratios, and I am weary of GM's PCM being year-sensitive to components relating to transmissions. I do know for a fact, however, that in 2003 the electrical and some mechanical pieces were changed in the 4T65E, so if the transmission is a 2003+ then it is not compatible. I would think that, since 3.8 Grand Prix's went from 4T60E to 4t65E in 1998, that 98-02 4T65E transmissions will work for your car. But I would check on a W-body specific car forum such as clubGP

Will a 99 2dr gtp transmission fit in a 01 gtp 4dr

Will a transmission from a 2003 grand prix work in a 2000 grand prix gt