Not sure if anyone has an answer for this one. I have a 2007 3500 mega cab single rear wheel truck, and from 60 m/hr and up I have a very strong vibration. I've changed all the u-joints except the front wheel input ones, balance the rear shaft, replaced the front drive shaft, balance all 4 tires, new steering stabilizer, new ball joints, front hubs, new brakes, new shock. Starting to run out of ideas. Anyone have any more?

 

The front axle shafts and driveshaft turns all the time so it could be those.