Since you recently had a regear check for loss of motion at the pinion. Chock the front tires, jack up one side of the rear axle & put on jack stand, transfercase in neutral.
Rotate the lifted tire forwards and backwards while watching the driveshaft, driveshaft should change directions immediately and the pinion flange should not move in or out of the differential housing at all. You can also turn the driveshaft by hand and actually may have a better feel for it there. It doesn't need to be rapid changes in direction or even lots of spinning, just enough to feel or see if there is a void where power wouldn't be transferred when changing directions.
Grab the driveshaft near the pinion flange and forcefully push and pull it; left, right, up, down. It should not be able to move, check it at the transfer case flange too.