So in my search to find the vibration I jacked the truck up in the garage, put the rear diff on some jack stands. I then put the truck into gear....... no this is not where it falls off the stands and drives through the house <img src="/forums/images/graemlins/lol.gif" alt="" />. Anyway the wheels spin true, the driveshaft seams to spin without any sign of vibration, but there does seam to be come clunking coming from the center differential. Now I only had the truck doing 1000 rpm so i was only reading 50 kph but the clunking seamed to be coming from the center diff. I shut the truck off and took it out of gear. I felt for backlash on the input into the diff and there was very little. I would guess I could move the driveshaft back and forth less than an 1/16 of an inch before I saw movement in the tires. Now was the clunking due to the fact that the truck had no resistance to movement? Any other ideas? I guess I will not know till I pull the diff out and have a look inside. Has anyone here rebuilt one of these before?