I just got my truck repaired from front end damage. It now ALWAYS runs as if it's cold. it's louder with that hollow intake sound and very slight vibration that used to go away when warm. Also it doesn't smoke as much when I floor the throttle. The local dealer put it on a scope and says it's normal. Any Ideas?

Stock 2006 GMC Duramax 6600 LBZ

I need a better mechanic.