cutlas rough shift into overdrive

i have a 94 supreme . the rpm drops abruptly about 500rpm as the car reaches the last shift at about 50 mph. giveing a jolt . it has just started this and has about 4500miles on the transmission fluid. i have tried the reprogram procedure after reconnecting the battery. this did not help.i have also replaced the upper engine tq links (dog bones).this smoothed it some .but its still jolts when shifting.also i do not have the check engine light on. the light test good. i have always maintained this car. 3.1 liter 4 year old transmission from ammco. appreicat any help i can get.

It sounds to me that your last gear is slipping alittle bit.

Or maybe the torque converter. Thats when it locks up, around 45-50mph depending how much your stepping on it. There is a plug on the upper front of the transmission when looking at it from the front of the car, I can't remember what color it is, but i think there is only one, unplug it and drive it up to that speed and see if it does it. If it don't then you narrowed your problem down to either the converter itself or the solenoid in the trans. Just a thought.