This truck has 300,000 + miles and was having trouble going into 4 lo. I read manual and put it into neutral and then into 4 lo only to have it lock in 4 lo. I have attempted all the rolling and reverse tricks and will not go into 4 hi or any other transfer case gear. The switching motor sounds like it is attempting to move with no results...
The truck needs to detect neutral and is required for shifts in and out of low range. Put into 4 wheel high then go through the the shift sequence P-R-N-D-N-R-P, repeat this a few times and see what happens. It may take many tries at this procedure.
If this doesn't work then at 300,000 miles I would have the switching motor checked out. It could just be to weak to push it back into 4 wheel high.