What am I doing wrong? Reading on the board I see people getting 17 to 20 mpg on their Duramax. I have 21,000 on mine now. I have installed a Superchip programer that I run on the safe tow mode. Performance Tow and Performane Mode did not help mpg at all. I am running stock exhaust, with a K&N air filter. I soft foot the truck trying to get good gas mileage. I am running 18in tires, but nothing wide or heavy. I would love to get 17mpg!
I generally stay around 14.9 - 15.5 @ 70mph. Running stock I get 14mpg. When towing a 7000 lb, 30' toy hauler I get 12mpg @ 70mph. I have tried 65mph and it doesn't increase that much. Maybe half a mile per gallon. Other Duramx owners have told me to get the Bulldog programer. Can anyone tell me if it will make a difference or am I expecting too much? Will the exhaust make that much of a difference? Oh, and I run my tire pressure at the max. setting. On the rare occassiions that I have put my foot in the truck it runs great!!! I do see a lot of black smoke, but only when I put my foot in it. Any suggestions.

Thanks everyone. This board on the people on it are a pleasure to come to.

Larry