I have a 1998 grand prix gtp and im haven some trouble. I think the thing that tell the trans to downshift from drive when you touch the brake is messed up and not letting the car be driven in 4ht gear (drive) lets say im cruzin down the road 55mph and i shift into drive and let off the gas it drops rpms and goes into drive. if i then downshift the rps jump up just like drping a gear and you can feel it. same thing if i was driven 55mph in drive and let off the gas it will upshift into drive but the second i touch the gas it goes right back into 3rd instantly and its even hard to notice at all that it does this. when i bought the car i drove home over 100 miles and never even noticed anything wrong! it dont make any noises dont act at all like a slipping transmission ever! and also i should add that my shift lock is not working and that also works off sensors off the brake peddal. just like the downshift of trans when in 4th gear (drive) and tap the brakes ( it downshifts) and im thinking this MAY have somthing to do with why my car is never given the opertounity to slip or be driven in 4th gear! and if i was right what an awsome post this would be an a huge help to the grand prix comunity as i will post results of anything that helps even if i do end up tearing the trans apart. thanks everyone