Well I got into a sticky situation yesterday. I parked on some dirt for about 30-45 minutes and my truck sank in a little. When I went to leave it wasn't happening in 2WD. So I though no sweat pull back the "magical lever"......nope!
Got out and started checking things. Here's the list so far:
Vacuum lines @ the crossmeber where they plug into hard lines
Big 4 Vaccum line on top of X-fer Case
Vaccum lines at the frame above front axle where they go from hard to rubber again.
Vaccum lines at the CAD unit on the front axle.
Vaccum lines in the engine compartment (Thanks for walking me through that JR, there's too dang many up there)
After all that it still didn't work, and the 'ol "When in doubt........" didn't work either!
I ended up pulling the CAD unit off the front axle and sliding the collar over manually. As soon as I did this and attempted to pull out I heard a loud
BANG! 
I stopped, checked the collar and it appeared to have moved over even more and locked in place. Tried it again and still no 4WD. All this time also the 4WD light on the dash never came on.
HELP!