[Blued and Painted]

Sounds like not your average vibration so I'll throw some things against the wall and see if anything sticks.

Hub centric wheel balance on a lug centric or uni-lug wheel. Lug centric balancing adapters are available.

Drive shaft to long. With the weight on the wheels, you should have enough clearance to flip the rear joint out of the pinion yoke.

Some have observed the factory drive shafts may look like a jump rope going down the road. Check installed run-out at front, rear, and middle.