94 GP Tranny

My 94 Gran Prix has a problem when trying to accelerate in O/D. The car starts shaking and almost feels like the tranny is going to fall out. It shifts fine both up and down and cruises in O/D with no problems. If you step on the peddle a little bit without kicking down the tranny you get the vibration. Any clues???

sounds like the TCC lock-up solenoid isn't unlocking the converter fast enough. this could be caused by dirty fluid, a faulty TCC solenoid, or a throttle position sensor that the engagement tangs are getting worn causing slop between it and the throttle shaft.