air vent close when i accelerate on freeway on 1996 Dodge Ram 2500

my air works good but i notice when i am on the freeway and accelerate quickly the vents shut until i let off the gas.

Asked by for the 1996 Dodge Ram 2500
This is indicating a vacuum leak in the climate control vent system. The airflow to the vents is controlled by vacuum controlled diaphragms, and if there is a leak, this is the symptom.