Have you checked the clutch master cylinder? If a bearing in the tranny or t-case were dry you'd get about 10 miles before it started destorying other things. Have you made sure all the bell housing bolts are tight? If the rear end is able to move around and you have driveline vibrations, definatly inspect the rear u-joints. It only takes a mile or 2 of high speed driving and bad u-joint angles to kill a joint.