This truck was getting 20 from day one. After I bought the Bully Dog the guy who sold it to me told me he has seen trucks from previous customers get 24 to 26 after the install. Maybe the calculator I am using came from eastern Oklahoma and is just plain dumber than F**K. I am sorry that you are having a hard time believing this but I have filled it up several times over the past 6 years and 180,000 miles so if you don't believe it than tough ****. We have a contractor out here doing work for us that has one getting 16 to 18 pulling his backhoe and trailer.
I'm trying to be civil but I can tell your getting awful hopped up about this. I work on plenty of diesel engines, I don't know about you but I drive diesel everyday, work on them constantly. I'm not going to argue with you about the subject because obviously your misinformed especially seeing as you are using bully dog. Anyone that knows anything about the Duramax would be running EFIlive.