[TwoThirtyDirty]

Losing vacuum when the truck warms up for some reason maybe??? Drive until the 4WD does not engage, then pop the hood and check for incoming and outgoing vacuum at the VSV valves per the pic. The hoses marked with red arrows are incoming. Check incoming vacuum by pulling both hoses, cap one with your finger, check for vacuum at the other. Check outgoing vacuum by pulling one hose at a time and checking for vacuum at the plastic nipple (blue arrows). If hub lock and 4WD are switched off at the dash, vacuum should be present coming out of the top VSV. If hub lock and 4WD are switched on at the dash, vacuum should be present coming out of the bottom VSV. If vaccum coming out of the VSV is not as it should be, could be indicative of a valve problem or electrical problem. If you reinstall the outgoing hoses backward, the 4WD dash switch will work backward. Shot in the dark...HTH.