07 EL XLT 4x4 w/ 18"s and 3.73s sees about 16 average and 19 to 20 on the highway. If you can get non ethanol gas it makes about 1 mpg difference on E-10 vs regular. This is also on 89 oct (that's all we use in our fleet trucks).

I'd expect that the 10's might get .05 mpg better then the 07 to 09 due to the electric fans.