correcting pinion angle after lowering rear

[shifty]

i lowered my '03 GMC Sierra and I had to use these little pinion shims from Sir Michael's. they were 2º of adjustment in the angle per kit, one shim per side. i think it was 2º specificallly for a 2/4 drop, but obviously the drivetrain is a little different between the two trucks.

the vibration you describe is something i hear about when people lower without adjusting pinion angle.