Yep...... the rim size itself isn't gonna impact MPG itself, depends on what size tire diameter you have.

I get 18.5 basically all the time, I have 305/70/R16 Mickey Thompson MTZs (33" X 12.5") and never run faster than 75 on the eway, take it easy off the line, and keep in mind mashin the pedal just sucks up the fuel.

MagnaFlow CAT back, Air Doc Intake, and PCMforless tune all help.

A CAT back exhaust system is a bolt on exhaust from the catalytic converter back. Quality kits will be made of Stainless, usually have a lifetime warranty, TIG welds, and mandrel bends to increase exhaust flow. More air out, more air in = more power making capability.

 

I also didn't notice a difference going with 20"s. The Nittos I'm running now just aren't good for Colorado snow, but are awesome on dry anything, as well as mud. They just float a bit too much on snow for the mountain trails up here. No gas mileage diff tho. Still get the same 17-18 depending. The handling is a bit different than the thinner stock 33"s, but felt normal after a month or so. I'll try to upload a couple pis., one front one rear to show the look of 20"s on it. (20x9 KMCs with 305/55/20 Nitto Mud Graps) Looks good to me. Totally tears up the trails too.