Literally just had this issue, but it was ujoints in the rear shaft. Another friend had the same issue with new ujoints, and it turned out they just weren't "seated" properly, and the straps weren't quite on right. Might pull the shaft and rotate 180* also.
EDIT: To completely rule out the rear shaft/diff/axles, pull the driveshaft, run just the front axle on jackstands. That might narrow it down to the trans/tcase.