Waasssuup! My name is Russell and I hail from San Diego, CA. I just took receipt of my 71 K5 blazer 2 nights ago, and it has issues. It has a SEVERE driveline vibration in the rear. I removed the rear shaft and put it in 4x and the vibration went away indicating a problem in the rear... The u-joints were used, but not wrecked, they were in decent shape. It has a 4" lift, and this is where I think the problem is... There are no pinion alignment shims under the lift springs, so the angle appears to be negative! I just picked up some 6 Degree shims and hope these do the trick. Any comments, suggestions? Thanks!