Well, I've seen a lot of people asking this question, and I would like to share a few findings I've found. And maybe people can share their findings. I've done the following to my truck to attempt to get better fuel mileage. Cold Air Intake, Throttle Body Spacer, New Spark Plugs, New Spark Plug Wires, Dual Exhaust, Fuel Filter, Synthetic Oils, and getting my EVAP Valve and compressor cleaned. I've noticed a huge increase in my gas mileage! But it all went to crap when i put bigger tires on. I've also found a few other reasons how to increase your gas mileage. Drive Smart Aggressive driving (speeding, rapid acceleration and braking) wastes gas. It can lower your gas mileage by 33 percent at highway speeds and by 5 percent around town. Sensible driving is also safer for you and others, so you may save more than gas money Fuel Economy Benefit: 5-33% Observe the Speed Limit While each vehicle reaches its optimal fuel economy at a different speed (or range of speeds), gas mileage usually decreases rapidly at speeds above 60 mph. You can assume that each 5 mph you drive over 60 mph is like paying an additional $0.24 per gallon for gas. Observing the speed limit is also safer. Fuel Economy Benefit: 7-23% Remove Excess Weight Avoid keeping unnecessary items in your vehicle, especially heavy ones. An extra 100 pounds in your vehicle could reduce your MPG by up to 2 percent. The reduction is based on the percentage of extra weight relative to the vehicle's weight and affects smaller vehicles more than larger ones. Fuel Economy Benefit: 1-2%/100 lbs Avoid Excessive Idling Idling gets 0 miles per gallon. Use Cruise Control Using cruise control on the highway helps you maintain a constant speed and, in most cases, will save gas. That's only if you are driving on mostly flat roads. If you are driving in hilly terrain, using cruise control typically causes your vehicle to speed up faster (to maintain the preset speed) than it would if you were operating the accelerator yourself. Before you push that cruise control button, think about the terrain ahead. Engine Maintenance Use synthetic oil in your car to save on average 5% gas. Extending oil change intervals can be harmful to the life of your engine and the fuel saving benefits are lost as oil gets dirty. If you cant use synthetic, choose the lightest oil possible, 15-30 rather than 20-50. Exterior Keeping your car washed and waxed improves aerodynamics and therefore affects fuel economy. Engineer Tom Wagner, Jr. reported to Stretcher.com (as in stretching your dollars) a 7-percent improvement in fuel economy, from 15 to 16 mpg, during a 1,600-mile road trip. Ventilation Running your air conditioner does cause your vehicle to consume more fuel, but driving with your windows rolled down can be even worse due to the increase of drag on the vehicle. If you are driving slowly, such as around town or in city traffic, then you are better off leaving your windows open, if at all possible. For highway driving, roll up the windows and turn the air conditioning on. The SAE found that most vehicles were more efficient with windows down until a cruising speed of about 65 mph. Tires Keeping your tires inflated to a proper air pressure, when your tires aren't inflated to the proper pressure they're less “round” and require more energy to begin moving and to maintain speed. An informal study by students at Carnegie Mellon University found that the majority of cars on U.S. roads are operating on tires inflated to only 80 percent of capacity. According to their findings inflating tires to their proper pressure can improve mileage by about 3.3 percent, whereas leaving them under-inflated can lower mileage by 0.4 percent for every one PSI drop in pressure of all four tires. Engine There's many things you can do for your engine that will help with getting better MPG, one of the most popular is purchasing a Cold Air Intake, this allow your engine to take in more air, that's at a colder temperature to have the optimum fuel air mixture, thus increasing your MPG. Also, getting a high output exhaust will increase your MPG, less resistance for your engine to push the air out. From personal experience, some may say otherwise, getting a throttle body spacer, made a SLIGHT(you wouldn't notice if you weren't looking for the benefits) difference in my fuel economy for the better. Also from personal experience I've noticed getting new spark plugs, increases the ease of starting my engine, and gives a light increase in fuel economy, it does this by having a larger spark at the peak of your power stroke, giving better combustion, giving more power per combustion, and you know the rest, burns more of your fuel, that would have otherwise been put out of your exhaust. Fuel Fuel may contribute to fuel economy, make sure to experiment at different gas stations. Some gas stations may get fuel from the bottom of the barrel, low quality gasoline. Some gas may seem to burn more efficiently in your engine. Be sure to experiment! These are ways I've found out, or ways I've been told how to increase your fuel mileage. Share yours please.