4-Runner Vibration

I just finished a complete rebuild on my 90 4-Runner, V6, 4WD. Started up within the first couple of minutes and seems to run very smooth. The problem is, when i accelerate over ~25 mph it starts to shake like somethings wrong with the drive train. Any suggestions? Could it be the drive shaft not matched to the transmission or the rear end or bad U joints? Or worse, something with balancing the crank or torque converter? I had the cylinder bored, turned the crank journals, and installed new pistons, and bearings. Any suggestions? Thanks, Gregg