I recently bought my truck and gave it a tune up. Before I replaced the air filter with a factor Dodge (Cost too much) I noticed the vacum gauge was at about 7 inches of Mercury (correct term?). I thought this was just due to a filled up air filter. The on that was in there was a K&N I tossed it because I didn't feel good about not being the one who had maintained it. Anyway back to the story, with a new "Dodge" filter it still draws down after a "WOT" wide open throttle movement. Is this normal I checked for restriction and none found. Sorry about the long post after being a mechanic for a few years I think you need all the facts to make a call!!
