I tried so many things on mine I lost track of them all. Check the tail shaft bushing on the transmission, if its loose the drive shaft will bind when under a heavy pull. Mine was a vibration but not due to a balance problem, it was more of running/tune up type of problem, it just seemed like a balance vibration.
A torque converter can get out of balance if it throws a weight off, but you should feel it at the same rpm in gear or out. A clutch should do the same. I found if I drove in low gear, I could get the vibration at the same rpm, only not as bad, It was really noticable pulling a long hill where the engine was working hard.
Check the drive shaft really good for missing weights or damage. Grab the front u-joint and really pull on the tail shaft bushing, also make sure the yoke is in the bushing all the way, it should be if its a factory correct driveshaft and the ride height has not been altered. Joe
