If you don't have a mech. stethescope, a long screwdriver will do. Chock the truck and jack up the rearend, SET ON JACKSTANDS.

Start truck, put in gear after idle kicks down, so the tires spin. Listen to the pumpkin; gears should run smoothly. If it's getting worn out, the noise will be uneven. Hope that helps a bit.

sounds to me like you might have bound a front hub
jack up the right front tire and rotate it while in the air and see it the cv shaft rotates with it. the front wheel driving on the pavement shouldn't have effected it much.

you may have driven the pinion back into the third member crushing the crush sleeve and damaging the bearings or something.

check the rear third for slop
and check that the pinion won't slide in and out of the third. there should be very little play
and should be no front to back/ or in out play to speak of
and the shaft shouldn't rotate much.

that's about all I can think of.
except the front hubs being auto one may be sticking
but you should be able to tell by the front cv shaft. you may want to service them.

is it unlocked
I don't have auto hubs on mine so ???
but is there a proceedure to unlock once your done wheeling

you may have finished off a cv shaft that was already worn out.