After numerous trips to the dealer who tried to fix my shudder by replacing the driveshaft, using shims, etc. I decided to tackle the matter myself. They told me that hauling a load or pulling a trailer lowered the rear end and caused the drive shaft angle to change causing the vibration. I went looking and discovered air lift supports. They are adjustable by air pressure to level the truck to compensate for the load. They fixed the problem and I just ordered an in cab control to adjust them from inside.