Maybe a combination of things. Because you say vibration developed on trip that somewhat eliminates incorrect driveline angles. There must be some angle of tube/shaft between u-joints, they'll quickly destroy themselves or other parts if they're too straight. If by any chance you slammed/lowered the truck that can mess up driveshaft angles and cause failure. Sorta doubt you'd lower a 4x4, but stranger things have happened, can't tell from here.

Many or most of these driveshaft tubes have a balancing weight or washer welded on tube or on yoke forgings that are welded to tube. Check that it didn't toss a weight.

Tube must be straight end to end, might chuck it up in a lathe and check the runout, doesn't take but a few thousandths to screw things up. Not unusal on a 4x4 running hard around big rocks or berms.

Also could be the combination, including a transfer case input shaft that was already stressed in the past with metal fractured or crystalized from some hard running or abuse, plus some badly worn t-case bearings [?], plus a driveshaft that isn't quite straight, and maybe add in a lost driveshaft balance weight, or a u-joint failure [maybe a cheapo replacement?] and/or badly worn or ovaled u-joint yokes. Then some spirited driving brought on by thoughts of Carlisle - something's gotta give - snap! bye-bye t-case...

Hope this happened AFTER Carlisle that you got to see the show, must be really cool!