95 4x4 won't shift

i have a 1995 v8 dakota 4x4. the transfer case was rebuilt and tranny tuned up 2 years ago. no problems shiftng until now. the 4x4 shift lever will not stay in 4wd mode. the lever will move but won't engage. no problems or noises with the tranny while in 2w mode. the 4wd light doesn't go on either. a friend mentioned a possible vacuum leak in the front axle but i wasn't able to locate anything. thanks in advance.

the got rid of the front axle disconect in 93 I think so there should be no vacuum lines going to the axle. sounds like maybe a shift fork in the T-case is bad, or the T-case is just plain totaled