I kind of agree on the interlock thing. With the shifter removed, I would try to move the 2wd/4wd shift rail back and forth and then try the hi/N/lo rail again while pulling 2wd/4wd either direction. The other thing I'd try is removing the shift detent springs and balls and trying again. This is stuff you should be able to do outside w/o pulling the t-case. You'll probably need a FSM to figure out what bolt/where to remove though.

Also, if there is gear grinding sounds when you try to shift back to 4-hi, then its probably not the shifters and probably has something to do with the shift collars inside. You could have broken a shift fork or something and its not sliding the collar evenly and therefore doesn't want to engage...?

One great resource to call would be Marlin @ Marlin Crawler. He may have heard of something like this happening before. I remember reading about something similar with the (v6?) transmissions that if they get jarred at a certain point they can get stuck in a gear (reverse?). I think usually that happened when the tranny was out and set on end though. Your jerk in reverse maybe could have done something similar.