Try this: jack up one rear tire off the ground, place range selector in neutral, 4x4 disengaged, ENGINE OFF, and try rotating the wheel by hand. If you have gear problems you should be able to feel it. You can also play with the diff lock while the wheel is off the ground, get an idea how it engages / disengages.
thanks Mike - great suggestion.
i had it up on jacks this weekend to put water ballast in the tires.
mine is a gear drive and not HST. the shifter was in neutral but range was in "4" - the shuttle was engaged in the forward position. 4x4 was off. i did not notice an gear troubles or noise when rotating the wheels to get the valve stems to the top.
it was still somewhat stiff to rotate the wheels around but that might just be because i weigh +/- 130# and have Muppet arms...
i did not think to test the engagement of the traction lock while i had it up. i'll try that this weekend when i use it to work on my old truck project.
ben