Ladies and gentlemen I'm a freaking idiot, the transfer case range lever was just ever so slightly out of high range. I must have bumped it when I parked at last. I am incredibly embarrassed, call the good friend of mine Jason and he set me straight.
First off, God doesn't make junk... Don't consider yourself an idiot.
And then a little
SAFETY NOTE regarding the M35A2 (and variants):
When parking the truck, disengage (in NEUTRAL) BOTH the transmission AND the transfer case. NEVER leave these Multi-Fuel Engine equipped trucks with the drive train either partially nor fully engaged to the engine. the Multi-Fuel engine CAN START with very little motion induced through the drive train!!! AND these engines CAN START in "forward" or "reverse" crankshaft rotation, too!!! This will result in a 13,000+ pound, driverless DEATH MACHINE for anything that happens to be in its way.... people, animals, structures, vegetation... ANYTHING!!!
By adopting this tidbit of wisdom as your SOP (Standard Operating Procedure) you will also prompt the ACTIVE ENGAGEMENT of the transfer case each time you wish to move the vehicle, thus precluding the SANFU that you recently experienced.
Unlike vehicles with other types of powerplants, these trucks ARE NOT to be parked "In Gear" to keep them from rolling away. They will - either because they're parked on a hill or by being bumped - instead become VERY UNSAFE because it was left "In Gear".
Instead, set the PARKING/EMERGENCY BRAKE.... AND, use Wheel Chocks, too.