Got back from my trip out west, took the truck to the dealer and they said my egr valve was bad. They said it was 40% held open. Would that affect my fuel mileage that much? If you did not read my other post I have a 04 250 crew with the 6.0. Went to Montana from Wisconsin for a snowmobiling trip. Pulled a 4-place open trailer with 4 sleds. Trailer, fully loaded, weighed just under 4,000lbs. At best I got 9-10 mpg. Havent driven the truck enough since Ive been back to see if it solved my white smoke problem.

 

Egr can drastically effect fuel mileage. Being stuck open 40% should have caused a few other symptoms also.