Although every year it takes me months to accustom myself again to drive the rig like it's a train, I see fuel mileage increase from around 12mpg all the way to 14 and 15mpg on my D-250 carbureted 1986 fuel-driven truck. Some things I have done that helped: Installed 8mm Taylor High performance spark plug wires Installed High Performance cap and rotor. Installed Flame-Thrower High Performance ignition coil. Installed High-performance air filter. Installed double-platinum spark plugs. Removed tailgate and replaced with a net. Doing the above increased my mpg by around 2 miles per gallon (around 20 percent). It also increased power considerably, which makes the next part tough: The next part is in the driving. Year after year I practice day in and day out to drive nice and easy on the throttle and accelerate about as slow or slower as a fully loaded 18-wheeler. I fear say the biggest drawback is driving the rig like it's a car, and also thinking that since it has a trailer it needs to PULL so we automatically give it more gas or the same gas longer. The trailer will come along without PULLING. It is hard to measure since the motor is doing the work, but if you've ever ridden a bicycle with your child in a seat, you can figure this one out by pedaling normal, you hardly feel the weight but start to push the pedals and oh now you can feel it - same principle applies: Try not to make the truck feel the trailer, but let it come along on its own by being very light on the throttle. Truth be known, less gas is the secret, not more. The rig consumes the most fuel from 0mph accelerating, and I have learned this is the time to give it the LEAST amount of fuel. Accelerate very slowly and then give it just a little more once you get up to 15 or 20 mph and then wait while holding the pedal lightly pressed, let the truck work its magic mile by mile per hour, I know I am doing the right thing when the needle is barely moving upward. Let it take a few minutes if that's what it takes, the slower the needle moves, the better the mpg. Use terrain to your advantage: Allow the truck to slow some going uphill (never accelerate uphill, and if you have to then stay below the speed limit), and let OFF the gas some just before you crest the hill. Of course, use downhills to build up speed but again, real nice and easy. Predict traffic lights and don't make the mistake most folks make of hurrying up to the light to stop and wait. Instead, slow down early and coast most of the way: You're even better off to slow down to 15-20mph a ways up the road and then sneaking up on the intersection so long you don't have to stop, that is the idea. If you're not sure whether the light will be green or will turn red, you are better off slowing down in case it turns red than speeding up to try and beat it. Trust me. The true secret to driving is to learn to control your speed using only the gas pedal. For example, I almost never use the brakes on off-ramps, instead I let off the gas early enough to slow the vehicle down with coasting. At the ON-ramp, use the full length of the ramp to build speed slowly, use some shoulder if you have to but try not to (it's illegal for one, dangerous for another due to roadside debris) but you get the idea: use that ramp to build speed, and be ready to merge below speed limit (I usually merge doing 35-40mph into a 55-65 zone). If you move slow and your turn signal is on, people will see you - The more you drive this way, the more they know your style. In traffic, hang back: Everybody is always trying to be number one. The easiest position to achieve in this race is last, and once you're last, fall back some more so you have SPACE in front of you: Use this space when traffic in front slows down so you can coast instead of using brakes. From what I have seen, the time saved by rushing is not worth the money spent on fuel, brakes, tires, and everything else that wears and tears at over twice the rate as when taking it real easy, not even when time is worth 60 dollars / hour, not even then.