It's nice to see this not in the Unicorn Corral. 11% is a more realistic claim than some of what gets touted there.
Start a garage entry for your ride. It's possible some of the (more talented than mine) eyes looking over your results will spot a detail that can steer you to more positive results.
Finally, go look at Diesel Dave. I don't know what the hell he's doing but he's got a truck not too dissimilar to yours and is pulling in 50mpg. I think that might be what Lone Starr would get if he poured concentrated
Schwartz into the fuel tank.