i had the same issue on my SR once in the last 2 weeks. hasnt happened again. my mazda also has the same issue where it tries to engage the front diff (has the same basic design as the montero) while driving. never did figure out what was causing it so i just leave it locked now and leave the t-case in 2wd.

87 Montero V6 SWB auto. dual bouncies
89 Montero V6 SWB 5 speed. dual bouncies
97 3000gt VR4 upgraded turbos, 10:1, E85
91 Stealth TT twin 18Gs, cams/heads, E85
03 cobra lightly modded <img src="/forums/images/graemlins/lol.gif" alt="" />
91 MR2 turbo