I've heard of and experienced it popping out of 4 low due to interference from the body after a body lift. I could shift into low but with the slight movement of the body over the frame the body would come into contact with the transfer case shift lever and knock it out of gear. If you haven't checked that you may want to. Pull up the shift boot and take a look.

Any time I see that someone has a body lift I tell them to recheck their mount bolts. So take that for what its worth. I had a bad time with them.

Have you always been in MA? I don't remember seeing you as a fellow zu member of the communistwealth before.
--jeremy