I have a 1994 skylark. Runs fine; accelerates good & smooth. Once you get goping though, at about a 50mph cruising speed when if shifts to overdrive (rpms drop to ~1800) it really bucks (shudders)up a storm. I replaced the top motor mount which was bad, but this didn’t help a lick. Any suggestions?
I’m not an expert, but I’m going to suggest the problem is in the torque converter lock-up mechanism.
The torque converter is supposed to lock up at a certain speed (usually 40-50 mph). If your vehicle is not locking up correctly, it might cause the symptoms you describe.
Just a guess.
Before you go doing anything with the transmission, have a drivability man look at it. A bad plug wire/plug would cause the same symptoms. Drivability issues are commonly mistaken for transmission problems causing the owner to spend many unnecessary dollars on the wrong component.
Let us know what you find out.