At 21.1 vs 19.2,if you drove the statistical 45% EPA HWY miles out of each years statistical 12,000 miles,over the 12-year life of the truck you'd save $ 1,063 in constant 2011 dollars ( @ $3.50/gallon ),and reduce carbon dioxide emissions by just short of 3-tons.
When the truck wore out the cap could go onto another pickup and do it for another 12-years on that truck, ad infinitum.
Nice parlor trick!
