Dodge 4x4 works sometime and not other times. 10pts best answer.?

My 01 dodge 2500 4x4 workes sometimes and not the next time it is becomeing VERY unreliable. I have adjusted the linkage under the cab and it still will not work all the time. When I am stuck in mud and engauge the 4x4 it feels like it is engaged at first and then it quits. 4x4 hi or 4x4 low both the same. After pushing and pulling the lever a million time it will engauge and stay engaged. The last time I got stuck the 4x4 did not work at first then it worked enough to get me out and I stoped after I thought I was compleatly out and put truck in park. I got out to ge tmy tools and got back in and the 4x4 would not work. I did not disengauge when I got out I left it in so something is screwed up and it pisses me off. When I need 4x4 I WANT 4x4 right then. Any ideas on what is the problem? Like I said before I had already adjusted the linkage so count that out. Best answer gets 10 points. Thanks