When driving at highway speeds my '94 Grand Prix (3.1L) will "buck" and "shimmy" every so often. By manipulating the gas pedal in either direction- I can get it to stop.
If I put the cruise on it seems to happen much less. It seems to do it when the car approaches an incline. A quick tap on the gas correct the problem (temporarily).
The Service Eng Light has come on a few times. (Unfortunately this is a transition car (OBD1-OBD2) and I can't pull the codes)
Does this sound like a failing Throttle Position Sensor?