What do you mean by that? Are you spinning the tires by hand and getting these results? Or are you running the truck and holding a tire when hitting the gas?
The easiest (and most destructive) way I've found to figure out where your drivetrain is failing, is start the truck, hold it down on the ground by pushing down on the roll bar until the chassis hits the ground, then give it gas until you see the drivetrain spin. Best done on grass so that if the front is fine, the wheels will spin. Then you can see if it's your rear diff internals or what.
Do you have CVD's on the rear or dogbones? There's a possibility that you either spun a wheel hex, busted a wheel hex pin or your CVD joint has something busted in it.
Doing the above test will let you see what spins and what doesn't when power is applied. Should help you figure out the issue.