As already mentioned the base model is a Borg-Warner 1356. The "-25" suffix is the specific model/version of 1356. A lot of F-150s and fullsize Broncos of this era should have the same transfer case, though I don't know the specifics of any minor changes that may have occurred (I'm a Chevy guy).
Make sure the shifter mechanism is not the issue. Follow the shifter back to where it hooks to the t-case, should be a little arm sticking out of the t-case. Unhook the shifter and manually move the arm to the different positions......if everything works okay the shifter is out of adjustment, if the issue stays then likely internal t-case issue.
Just remember to block the tires so you don't get run over when you shift the t-case into neutral while laying underneath it.
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