my car 1998 Grand Prix GTP. was running fine then all of a sudden i lost 3rd gear. it shifts from 1-2 just fine but then it revs up to about 3k rpm at 40mph then shifts to 4th gear. manually selecting gear on the gear selector does not put it in 3rd either. i let that go for about 3 months, and every now and then i will loose 4th gear and the car will be stuck into 2nd gear. usually shutting the car off for a while and turning it on will make 4th gear work again. but now all of a sudden i lost 4th gear and it wont come back at all. idk what happened to 3rd gear. if i were to floor it i could get the car to 90mph and the engine cuts out at 6k rpm. if i let off the gas some it shifts into 4th gear. is it in 2nd gear all the way to 90mph? seems like it to me. 90mph @ 6k... now i have a P0756 code for Shift Solenoid B performance. stuck OFF. sometimes from a stop it feels like it sticks into 2nd gear and has no 1st gear. so when i take off there is no power. is it just my solenoid? or is my 3rd gear totally gone as well? should i replace tranny, or is there any hope for mine? it was a rebuilt tranny and now has 230k miles on it. the tranny oil was replaced exactly 1 year ago and is now black. the fluid level is full. and the car acts the same whether it is cold or warm. Also, my performance shift button doesnt work, ive never had it on this car at all. any reason for this?
I better check myself into a clinic 
) Side cover is the painful part of the process. Gotta drop subframe and the side of the trans. Once it's off, the soleniod is a simple clip and it's out. 
