Don't jump on me, I need this vehicle for my business. 2004 Ford F150 with heavy duty payload package. 4.10gears/5.4L engine/4X2 I drive conservatively, rarely exceed 62.5mph on highways and coast and anticipate lights/traffic. My truck is rated at 13/17 but I think that's with a regular cab and the lowest gear ratio. my truck is a supercab(800lbs.+) and has 4.1 gears as opposed to 3.31 gears. I also carry a consistent 500lbs in the bed with spikes of an additional 500lbs once a week. regular driving gets 13mpg. I tried a fuel economy run which is my regular 50/50 city highway driving route but with a 100% commitment to maximizing my fuel economy and got a whopping 15.5mpg. I have to admit though, it was a painful experience. my question is, concerning gearing. how much of a mileage gain will I achieve if I change the rear end gearing on my truck to the 3.31 ratio. I calculated a drop at 62.5mph from 1950 rpm to 1600 rpm. will this make a difference in real world driving or is it just maybe 1mpg, which really is not worth it on a cost/payback basis. thanks in advance for any and all suggestions and, no, I actually do need this truck for work and yes, I would rather be driving my old crx.