Took the truck on a 200 mile trip over the weekend and noticed the ventilation air flow changing each time I opened the throttle to pass, etc. I know this subject has been covered before, but I can't remember if there was a fix for it or not.

 

Rexx, it can be a number of things that actually cause it, but it is the vacuum loss of the defrost door accuator, do a search, it sometimes is the checkvalves ,in which Dodge had a bulliten out on them, ,and alos the cannister, but also check the valve itself, first, it is often overlooked, you have to lay on your back, drivers side head as close to the center of the dash as possible look at the silver valve pointing straight up it has an arm on it about 3/4 inches long, and snaps on to the lever of the defrost door, pull off the yellow hose and pull down the lever, with one hand while plugging the hose nipple with the other it should hold the lever still PERIOD, no slowly goign bacK at all, after you check this you know it is fron the valve upwards towards the source..