When you tow you are supposed to turn the overdrive off. We still need more info about your truck; Yr, mileage, maintenance done on the truck, any CEL's. Also do not calculate your mpg by using your gas gauge. Your fuel guage could have went bad. Go fill up your gas tank, reset your trip meter odometer. Next time you fill up take the miles you have driven from your trip meter and divide that by the number of gallons you get the next time you fill up.
PRG Basic Suspension Package
XTP IMS, Gibson Exhaust, Airaid Intake, UpRev Tuned
N-Fab Nerf Bars, Bakflip G2, Line X Bed Liner