I have an '02 Duramax in a Chev Silv 2500HD 4x4 crew cab running 15w40 Amsoil and Amsoil air filter with a Superchip set at Performance Tow (BTW...the superchip made NO difference in my MPG at any of the 3 settings) - getting 17mpg in town -19 mpg hwy. at 75mph (average).

How can I improve the MPG?
Has anyone tried a scoup in the hood to force air in or a bigger exhaust to reduce back pressure?

Thank you in advance for your help! PJvH