Vibration over 65mph

With the car at normal ride height, peak under and see if the drive shaft yoke face is almost jammed against the tail housing. Also, try taking the shaft loose at the rear yoke and clocking it 180*. Have you tried putting the rear axle on stands and bringing the RPMs up to see if it is indeed the rear end, of something in the transmission, of engine.
I have in the past, but I’ll try the 180 degrees rotation to see if that changes anything.