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When my wife floors the truck or goes up a hill that requires a little more petal power the dashboard vents cut out and the defroster vent comes on. Got a vacuum problem some where but don't know where to start troubleshooting? It only does it when pushing the truck a little bit.
I would think you have a vacuum accumulator that stores vacuum to hold the various vacuum operated devices in place when the engine goes to full atmosphere (no vacuum) as happens when you go full throttle. Full throttle and there is no manifold vacuum. The cylinders are sucking and the throttle plate is wide open and getting all the air it can to the cylinders - you do have air flow in the intake manifold but no vacuum left foe the periphrials. i have heard of this on late model Dodges. The accumulator is either bad or not big enough to hold enough vacuum for your long full throttle needs.