It could be any number of things. The first things to check are the vacuum
switch ontop of the transfer case (the one you replaced a while back), the
actuator that switch connects to, (the diaphram located either under the
battery tray or on the innder fender behind the battery), and the vacuum
lines themselves (primarily the line from the intake to the vacuum switch
and the line from the vacuum switch to the actuator, the third is a vacuum
release (breather) for the actuator). Odds are one of those three is your
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