things to establish, is it axle wrap? put truck in park and try rolling it back and forth and see how much pinion moves up or down. if it does tighten u bolts and recheck
secondly, check driveshaft, inspect u joints and see how much the slip yolk has been pulled out. most people dont do any driveshaft work after a lift so your slip yolk sticks out farther which is more hurt on your trans and eventually can cause vibration, wear and whipping. pull driveshaft and check pinion. it likely still has a 10 bolt if it was anything like mine it hated life and grenaded itself after the pinion nut backed off completely.