Well i replaced both U joints on the rear drive shaft. The U joint on the end that connects to the differential was smoked. All the needle bearings in one of the cups where compeletly gone, i think the cause was the seal was torn and all the grease escaped. The U joint that is on the end of the drive shaft that goes into the transfer case seemed to be good but i replaced it just for good measure. Trucks is nice and smooth again, no vibrations and no shakes at take off. Hopefully i am good to go for another 100K