Great thread. I think this is what is wrong with my 923a2 t-case shifting problem.
I've noticed that when I turn the engine off and let the air out of the system a few pounds at a time, it gets progressively easier to operate the transfer case lever.
Also, with the engine off, air system pressurized, battery switch set to on, you can't hear anything happen when you press the button on the t-case lever. I think the transfer case interlock valve ya'll have been talking about here isn't working properly.
I think I will just disconnect it and cap the air line. High range is all the way on the floor, anyways so it's not like there's a risk of it slipping into neutral on me going down the highway.
FYI guys, the big 4 volume TM has a diagram with instructions on how to replace the interlock valve being discussed. 9-2320-272-24-1. Starting at page 3-392