Gmc acadia was bought in january 2008. has been back 4 times for propane smell that comes into the car from through the vents. it mostly happens when i stop for a red light. the fumes seem to back up into the car. catalytic converter and exhaust system was switch out but it continues to happen even after 7000 miles. have called gm corp as well as dealer to complain that the smell is making me sick. doctor notes have been sent to dealer and corp but still not resolved. i drive with my windows open even if it 20 degrees. *tr