Engine Vibration at highway rpm/speed

It doesn’t do it in nuetral its no the engine. Pinion angle or driveshaft phasing. You can mark the shaft and pinion yoke then take ot apart and spin it 180 degs. Then see if it changes the vibration. I had the same thrummm. Pinion angle and new/bal shaft took care of most of it. New tailshaft bushing?