Wow, I can't believe you guys get that bad of gas mileage. My first Toyota pickup was a 1990 standard cab deluxe 4x4 3.0 5 speed with factory 31" tires and I did the 2-1/4" cat-back on that truck too. I average 21 mpg and 24 on the highway with that truck. Maybe the exhaust makes that big of a difference, I know the factory pipes neck down to 1-3/4" or less in the bends.