This is somewhat of a common problem and tends to be more common on the eariler trucks that have a softer output shaft.
From the factory, the shift hub and the matching shift collar have a 2 degree taper that helps lock the t/case in gear.
After thousands of miles in 2 wd, and then shifting into 4wd, the worn hubs were mated to the unused 4wd hub.
This can result in a "locked in " condition which can usually be unlocked by shifting into reverse and working the clutch untill the hubs free up.
1980 Toyota - 1997 3RZ-FE 2.7l Engine, Turbo R151F 4.31:1, Triple Turbo Marlin Crawler Billet (2.28x4.70x4.70) = 1,148:1 Crawl Ratio, Marlin Crawler Twin Stick and Short Throw Shift Kits, 30mm H/D Output Shaft, High Angle Drive Lines, 5.29:1, ARBs, High Pinion Front, 25mm HD Billet High Steer Kit, 6 Pin Locking Hub Bodies, 86+ Wide Rear End, V6 3rd member, Chromolly Axles all around, 37" IROKs with Beadlocks, York onboard air - Rollbar air tank, Premier Power Welder, Marlin Crawler 4" USA-made Leaf Springs, Bilstein Shocks, et cetera....