i agree with heavyd same thing apply to a/c too i turn on a/c few in winter time too and webasto heater in sumer time too for few mts
i have 06 columbia detroit motor and i got problem of egr in colarado freightline did job but after that i never got same engine power back even...
same thing was mine 06 columbia and it cost me 400 canadian still i have half play and somebody told me to change tower still i have play cause it...
same i have problem if u have any idea just me know but i changed the air control valve now i dont know how much height i have to keep dealer says...