Finally taking my first trip with the Gryphon custom tunes and am impressed with the results. I was running a 91 performance tune (5.4l) and got 17.05 mpg (hand calculated) about 95% highway. This was running most of the way with the cruise on at roughly 78 mph. After seeing the ampg go up to over 18 mpg at one point when running about 65 for a few miles, I can imagine slowing down some would be much better. On a 420 mile one-way trip, I just can't bring myself to slow down any, though! I now have the 93 performance tune loaded for the return trip and will post the difference if any when I get home.