When I put the truck in 4WD hi it goes in, but then it will clunk and jump out and then go back in, in a sec. or two. I'll go a little more and it will do it again until It gets me stuck. It won't do it in reverse at all, it goes in and stays in, it is a manuel tcase if that makes a difference. It has been slowly getting worse and is now getting very aggrevating.

Sounds like either a linkage out of adjustment or a broken mount somewhere.