I replaced the transfer case this weekend (NP246) on my 99 suburban with a unit I found on craigslist, supposedly a factory rebuild unit. When I dropped my rear driveshaft I noticed the ujoints probably needed to be replaced. I took in to a machine shop and had them press in new joints. When I got it back and installed everything it had a "body" vibration at 50. Inspected the driveshaft and they had installed the rear u-joint incorrectly (it was VERY hard to move the joint, like it was binding). I took it back and they replaced both u-joints. Reinstalled last night and the vibration is better, but it still does it at 60-65. I took the front driveshaft out to verify that the front u-joints weren't bad and that was not the problem. Question: Could the transfer case be bad and causing the high speed vibration? Is it possible that the driveshaft could now be out of balance? I'm not sure what would cause that. Do the brass c-clips need to be installed at the rear diff cups that are strapped in? I didn't think they were installed when I took it out. Thanks for the help!