What fuel economy we can expect for Duramax 6600? I have bought a used Duramax 660. Current the truck is producing 17-21 mpg when driven empty. That is fine. I am not happy with the power. I guess replacing air filter can resolve this issue. My friend suggested me an airfilter (https://www.bcdiesel.ca/en/afe-stage-ii-cold-air-intake-replacement-filter-dry). He says it is a good one that helps the power and will not affect the mileage. How about this model? If you have some idea about this please share the reviews.