It finally stopped raining so was able to go out and troubleshoot the issue.
Engine running in 2-wheel drive in gear with clutch in/depressed no driveshaft movement.
Engine running in 2-wheel drive in gear the driveshaft spins but rear wheels do not
Engine running in 2-wheel drive in gear with OD engaged driveshaft spins but rear wheels do not.
Engine running in 4-wheel drive LOW in gear with OD engaged or out driveshaft spins and movement as if normal.
Engine running in 4-wheel drive HIGH in gear with OD engaged or out driveshaft spins and movement as normal.

So, based on the above it sounds like a broken axle. The odd thing was there was no sound or clunk when/if the axle let go. It was purring along at 50 mph (as much as a belching LR purrs) when it just coasted to a stop.