WildeOne

No hills here, sorry!

I don't know about the difference in MPG due the rears, but 4WD will cost ~ 2 to 3 MPG, due to the add'l weight (~500 lbs) and friction. BTW, 2 WD also gets you greater towing capacity, due to the lower all up weight. I haven't had any trouble towing a 9 K lb boat and trailer, including some launch ramp experience.

I have an '07 Expy 2WD and 3.31 rear. I consistently get over 20 MPG when not towing. Note that's with cruise engaged and a light foot on the gas pedal. If you get 4 WD , you can count on several MPG less. 3.73 rear would also a have a negative effect on MPG. Acceleration when not towing is adequate, but not breathtaking. It's an OK compromise given fuel prices. Local, short trip MPG will be lower ... I try to reserve this truck for towing and/or long trips, where it excels.