I think everything you have done narrows it down to transmission output bearing or t-case. Did you check that fluid level and condition?
The only other things I can think of is to make sure the front hubs are unlocked, make sure the front driveshaft isn't spinning. or remove the front driveshaft altogether.

 

I confirmed the fluid level and condition were good. It has auto-locking hubs so other than the having the 4X4 light on or off is the only way of knowing it's engaged.
I'd have to wait until spring before tearing into the transmission since the snow season isn't over. I still need to rely on it now.