I have been tracking my fuel on fuelly which you can see in my signature. I have the 3.21 and wish I had the 3.92. I spend 80% of my time driving freeway speeds around 75-80 MPH. I am on track to put over 30K miles on the truck in the first year of the trucks life. My old company work truck was a chevy 1500 with the 5.3 and I was averaging 13-14 mpg under the same operating conditions. All in all I am pleased with the truck. Highly recommend it over a chevy. (as a note, if you look at the fuelly and see the 8 MPG fillups, I was towing a 6000# trailer from Wyoming to the Washington peninsula @65-70 MPH, I got a lot better economy coming home going from sea level to 7000 ft).