Cadillac Repair: transmission, 20 rims, speed sensors

Question
hello i have a 96 sedan deville 32v northstar  139Kmils an just a few day ago my car started acking like it was going in netrual when i got up to 45mph it would just idle up then jerk into 4th gear then the service trans light came i got the filter an gascuk change but not when i get to like in the 40s it will just ill down to the low 30s what do u think the problems is im clueless i dont drive fast i called the dealship i got the lack from he says he think it might be the 20" rims that i have on there. but that dont sound right plssss help me =)

Answer
It is possible that your rims are causing your problem. There are speed sensors at each wheel that send digital signals as to how fast the wheels are turning and this information is computed into the computer in order to engage and disengae the electronic solenoids inside the transmission to shift the gears at the correct time. With these large rims on it the computer is getting false information as to actual road speed.