I have a 02 4 wheel drive extended cab 3 door S10. I just recently bought an installed rough country two and a half inch lift, before I put my new tires on I had a vibration, my tires were cupped and in bad shape. So I was hoping it was just the tires. Got my new tires installed and have the exact same vibration it was right about at 70 miles an hour, I noticed the pinion angle had changed a little more than I thought it would so I bought some 4° shims and install them. The vibration is different now but still there now it starts about 60mph below those speeds the truck drives flawless. Before I lifted the truck it drove perfectly smooth so I'm guessing it's the angle of the pinion or u joint ?

 

Your pinion angle is "backwards". The pinion should be pointing down slightly in relation to the driveshaft, not up. Ideally, the angle at the back of the transfer case would match the angle at the pinion yoke, but within a degree or two should work ok.

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