Without the key stock welded in, it's gonna be hard to diagnose much because the shift handle will flop around and fall in and out of its shift gate... I suggest removing the shift handle and possibly also the shift base and operate the shift fork with a medium sized flat head screw driver to be absolutely sure that it is unable to access high range.
The most common issue is that a Crawl Box cannot engage low range when the transfer case is in high range (due to an installation error of not modifying the transfer case's driver's side shift rail for use with a Crawl Box). But your case is the opposite which is strange indeed.
It's shift rail could be installed 180-degrees off, or it could have a rusted shift spring... Pop that shifter out and have a look inside to see what is going on.
Regards,
BigMike
