I got 20 mpg all summer long with my 88 V6 and I shift around 2500 rpm's. Clean your throttle body and even clean the air flow meter for starters. What size tires are on the truck? If they are larger than stock then you need to compensate for the difference in your odometer readings. My mileage does drop off a little in the colder weather due to higher idle but you're still pretty low.