Yeah Okay, I am driving a 2005 Cummins 5.9L. When I had 5" turbo back exhaust, and AFE Stage 2, running Mobil 1 Devlac I was getting 24mpg US, this is the honest truth. This seems to be where it ends as of yet. I have put in the the Techni-Cooler, & the Six Gun w/Speed Loader. I have no Change...