I have an 02 3500 Duramax with an Edge Performance chip, I can tell you even in an 8,000 pound truck 425 HP and 880 lbs of torque is amazing to drive. I get 18 MPG driving to work and back in 50/50 city/highway driving just 22 miles a day. I am sure they could get 40 MPG easy. With just the chip the 6.6 goes from 300 HP to 425 HP, I just wonder how much Edge will get out of the new Duramax?
Below is the link to the 6.6 chip;
http://www.edgeproducts.com/product.php?pk=49&pvk=131