Driving one day and all the sudden truck starts vibrating. Started shaking at 55-60. Thought I had thrown a weight off tire. Rebalanced tires and still vibrated. Changed all u-joints and carrier bearing in rear shaft and now vibration is at 30-40. Seems to be coming from rear. Also changed driver rear wheel bearing and put on a set of stock tires and wheels from another super duty and no change. No sign of a weight missing off shaft. Also no slop in pinion bearing. Any ideas? Gonna pull rear shaft off and take it for a spin. It's pretty bad.

 

I have similar vibration, thought it was tires. I'm replacing tires in a few months so I let it go. If you get it figured out please share!