4wd gets stuck

Ok, a few weeks ago I was hitting some trails in the blue ridge, and my 97 rodeo decided to get stuck in 4wd (hi). Finnaly got it out and didn't think much of it.
About a week after I was on I-95 and it suddently decided it wanted to be in 4wd again! I didn't touch the shifter and tryed to get it back in 2wd. After limping back home, I did a partial fluid swap in the tranny and put some lucas in it. Seemed to work.
This afternoon, I was playing in some mud and after the first run I coundn't get it out of 4wd, again. I moved the shifter to 2wd and decided while it was stuck in 4wd to run it again. It seemes that I got it out of 4wd when I launched the fount end.
Anyway, I would really prefer to be able to go back to 2wd without destroying my front suspention. Any Ideas?
By the way it is a 3.2L auto, with new shocks and a history of problems involving the mode switch. (normally I can clean the terminals off and put some new greese in it and it runs fine)
Thanks for the help.