reply>

The axle bearings migh thave been packed with too much in them, keep an eye on them, I did install tube seals so no oil should leak out. As fo gear whine, well it is an all aftermarket set up and it doesn't make it prone to wearing faster, or anything breaking, its a 9" good for over 600 hp. Is the vibration only on the jackstands? Or what mph does it come in and go out at?
My 1999 Silversado vibrates between 70-75 mph and I have been chasing that down from the day I bought it. U-joints, tires, turned rotors when I put new pads on and had them balanced while off my truck. I still get the passenger seat shaking at 70-75 mph. Go figure.