Well, if you want to be able to diagnose it without a scan tool (which is
quite difficult), we would need more info.  When you say "I am stuck in
4wd", what exactly does that mean?  Does it mean that the dash switch
4h light is "lit" and when you push any other position, the other position
light flashes but the shift is not completed and then it simply goes back
to the 4hi light on?  Is the front diff locked? (should be able to tell
simply
by how the truck feels when turning, ie: is it crowhopping?).

Even with this info, it's quite difficult for the average DIY'er to diagnose
these auto t/cases without a scan tool and some knowledge of how the
system works.

Ian