I won't say you're full of it. Just like the Powerstrokes, some of these IDIs seem to get incredible fuel mileage (16 city 20+ highway) and some seem to be energy hogs (<10 city or <14 hwy) and some seem to just be unremarkable like mine (12-14 city, 14-17 hwy) no matter what we do. 24 would be incredible though. I'd think you'd need an aggressive O/D and numerically low (tall) gears coupled with a light foot and light or absent loads. What's stranger is we haven't seemed to be able to develop a recipe that says do X, Y and Z if your primary goal is minimum energy use and least emissions.