1990 Grand Prix nasty transmission vibe

So here goes.

1990 pontiac grand prix, FWD, 3.1, Automatic transmission (http://www.ford-trucks.com/rx98192zju/kwldirect.php?kwid=527)has a nasty vibration while under load in every gear including OD below 3,000 rpm. In neutral it goes away, stopped it goes away, doesn't do it in park. As soon as you hit 3,000 RPM it's like somebody just turns the vibe off.

The vibration is constant in frequency and sound level from as soon as it shows up until it disappears.

Transmission (http://www.ford-trucks.com/rx98192zju/kwldirect.php?kwid=527)was fine until the car stalled out on my friend. He had it flat towed 30ish miles at speeds up to 50MPH. I sorted out the running issue for him, now this trans issue has shown up. I think it's internal to the transmission and is a result of the flat tow, but don't know for sure.

Any input would be greatly appreciated!

Justin

It sounds like the flat tow ruined the transmission. FWD transaxles are very sensitive to towing, and shouldn't be towed with all wheels on the ground, especially over 35 mph, for more than a couple of miles. I would suspect he wrecked the converter and/or front pump assembly.