I recently bought my first diesel, an 05 2500 hd duramax with a 6 inch lift and 35's and a AFE intake. When I bought it it had a sticky egr valve and a tear in the inter cooler boot. I pull a 10 ft cargo trailer every day for work. The first couple of tanks of fuel I was getting about 12 mpg pulling the trailer. Since then I repaired the inter cooler boot, installed an egr blocker plate, got a 4 inch exhaust, and installed efi live. Since then my mpg is 12.6 on setting 1 "optimized stock" and actually dropped to 11.9 on setting 3 which is the "llight tow" setting. The diesel shop said that my injectors are with in tolerance and I have no boost leaks. I am really ddisssapointed with the mileage especially after spending the money on mods with not much increase in milage. Does anyone have any ideas?