Had one at 70 mph on my b-body. Too much pinion angle. Reduced from 6* to 4*. Much improved. Prior to 6* it was less than 2* and it vibrated. Had to find the sweet spot.

‘72 Charger, 5.9 Magnum, Tremec 5 spd., Pro-Touring
‘14 Big Horn, Quad Cab, 4x4, 1500