Very nice work, I applaud your creative efforts. I had a 2003 AWD Safari that I camperized, but not to the degree that you have.
A few things I learned while I owned my Safari...
As you've noted, the transfer case is a weak point, especially the encoder motor. The Dorman encoder motors are not as reliable as the OEM version but much less expensive of course. I kept a spare encoder motor with me; as you know, they're easy to swap out.
If you haven't already you should probably change the fluid in the transfer case. Replace it with ACDelco AutoTrak II, do not use anything else or any additives. The fluid controls the friction between the clutch plates in the transfer case and does wear out over time.
Finally, if you continue to have transfer case issues, try replacing the transfer case control module (TCCM). It's found in the driver's side footwell behind the emergency brake pedal.
The 4.3L Vortec V6 is a pretty good engine, but does have a few weak points as well. Worst is that the gasket between the intake manifold and the heads will fail, allowing coolant to leak into the cylinders and contaminate the oil. If you don't catch this quickly the oil is diluted and leads to engine failure.
Enjoy it, I miss mine.