Let’s face it—your 8,000 lb. L5P Duramax-powered truck isn’t about to sip fuel like a hybrid, but that doesn’t mean you have to burn more diesel than necessary. Whether you’re towing, hauling, or just daily driving, a few smart tweaks can help you squeeze out extra MPGs without compromising performance, and while this article is focused on the particulars of the L5P, plenty of it can be applied to any diesel.

One of the best things we love about diesels is the fact that – to a certain degree – the more power they make, the better fuel economy they seem to produce.

By implementing strategic modifications and adopting mindful driving habits, you can boost efficiency while maintaining performance. Here's how:

1. Upgrade Your Air Intake and Exhaust System

The LP5 Duramax breathes well from the factory, but improving airflow is always a win.

• Cold Air Intake: A high-quality intake (like an AFE) delivers cool, dense air, improving combustion efficiency.
• Performance Exhaust System: The LP5’s factory system is pretty efficient, but a low-restriction DPF-back system can reduce backpressure, improving power and fuel economy.
• Intercooler Upgrade: A larger intercooler can help keep intake air temps lower, allowing for more consistent power delivery and better overall efficiency, especially when towing.

Note: Since the LP5 comes with a full suite of emissions controls, any upgrades need to remain emissions-compliant (unless you like expensive fines and warranty headaches).

2. Optimize Engine Tuning & Calibration

Modern diesel engines thrive on precise fuel injection timing and pressure control, and the LP5 Duramax is no exception.

• Engine Tuner/Programmer: A reputable tuner can optimize fuel maps, helping improve efficiency without losing power. But be realistic—don’t expect “80 MPG miracle tunes” from the internet, or a high performance towing tune to net you amazing economy. But a well-calibrated tune from Banks or Edge can yield modest but real gains in terms of fuel economy.
• Shift Strategy Adjustments: The Allison 10-speed (2020+) is already well-calibrated, but early 6-speed Allison models (2017-2019) can benefit from a transmission tune to hold gears more efficiently.
• Tire Size Adjustments in ECM: If you’re running larger-than-stock tires, make sure your ECU is calibrated correctly to reflect the real rolling circumference. Otherwise, your truck’s fuel economy calculations will be way off. If you’re running larger-than-stock rubber, that’s going to throw off your odometer and speedometer, and simply calculating off of GPS to get your fuel economy can make you feel better about your rig. For instance, on a first-gen Cummins build some years ago, we found the speedo was way off, and when we correctly calculated our mileage, we were at a pretty respectable 24 mpg.

3. Tire Pressure & Rolling Resistance Matter More Than You Think

Underinflated tires increase rolling resistance, forcing your engine to work harder—and burn more fuel.

• Check Your Pressure Regularly: Running near the upper end of the recommended range reduces rolling resistance without sacrificing ride comfort.
• Account for Oversized Tires: If you’ve upgraded to bigger rubber, your odometer and speedometer are now lying to you. Calculate fuel economy using GPS mileage to get real numbers.
• Low Rolling Resistance Tires: If MPGs are a priority, aggressive mud terrains will hurt. A good set of all-terrains or highway tires can make a measurable difference.
• Wheel Weight Matters Too: Heavier wheels mean more rotational mass. A set of forged or lighter alloy wheels can reduce strain on your drivetrain and improve efficiency.
• Proper Alignment: Misaligned wheels increase rolling resistance and cause uneven tire wear. Regular alignments can help maintain efficiency and handling.

4. Drive Smarter (It Actually Works)

Your right foot is the biggest factor in fuel economy. Yes, we all love spooling the turbo and feeling the torque hit, but keeping things smooth saves fuel.

…And don’t believe everything you read on the internet, or at least research things a little bit. For example, our Canadian neighbors use Imperial gallons, which are larger than ours. (Imperial gallons are 154 or so fluid ounces, whereas our more humble home-grown gallons are 128 ounces. When your Canadian buddy on the forums brags about his mileage, take it with a grain of salt…he’s cheating.) 

• Ease Into Acceleration: Hammering the pedal from every stoplight is fun but burns fuel fast.
• Cruise Control Is Your Friend: Holding steady highway speeds minimizes unnecessary fuel-wasting fluctuations.
• Limit Idling: The LP5 burns about 0.5-1.0 gallons per hour idling. If you're parked, shut it down.
• Use Tow/Haul Mode When Necessary: If you're pulling a heavy load, using the tow/haul mode helps keep the engine in the powerband efficiently without excessive revving.

5. Reduce Aerodynamic Drag

Your truck is shaped like a brick, but small tweaks can help.

• Tuck Those Tow Mirrors: If you're not pulling a trailer, folding them in reduces drag. (We’re looking at you, Cummins guys…)
• Cut Down on Unnecessary Gear: A bed full of random stuff adds weight and messes with aerodynamics. It’s foolhardy to think dropping a couple hundred pounds is going to impact fuel economy on a rig hitting the scales at four tons, but every little bit helps. There’s a real need to run with a transfer tank in many situations, but remember that diesel weighs about 7 pounds a gallon, and that 70 or 80 gallon tank represents a LOT of extra weight you might not need to tote.
• Trailer Considerations: If you tow regularly, a streamlined trailer makes a difference. There’s a reason semi-trucks run side skirts.
• Tonneau Covers: There are plenty of reliable reports of some economy gains with a well-fitted tonneau cover, whether hard or soft.

6. Use High-Quality Diesel & Fuel Additives

The LP5’s Denso HP4 fuel system runs at 36,000+ PSI, so clean fuel is critical.

• Fill Up at High-Volume Truck Stops: They cycle fuel frequently, reducing contamination risks.
• Run Additives: Today’s Ultra-Low Sulfur Diesel (ULSD) lacks lubricity, and even though the LP5’s fuel system was designed around it, there’s some value in quality additives like Diesel Kleen, Opti-Lube, or AMSOIL Diesel Injector Clean in terms of protecting injectors and optimizing combustion.
• Know Your Diesel Blends: Fuel blends change seasonally. If you’ve ever seen a 2-3 MPG drop in winter, it’s because of lower-energy-content winter diesel due to the anti-gelling agents.
• Keep an Eye on DEF Quality: Poor-quality DEF (Diesel Exhaust Fluid) can cause SCR system inefficiencies, which can lead to poor fuel economy and even reduced power mode if neglected.
• Check for Water Contamination: Water in diesel fuel can damage injectors. Use water-separating fuel filters and drain your fuel/water separator regularly. Don’t rely on the sensors to tell you when there’s a problem.

7. Regular Maintenance = Maximum Efficiency

A well-maintained LP5 burns fuel more efficiently and avoids expensive repairs.

• Change Air & Fuel Filters on Schedule: A clogged filter chokes your engine, hurting power and efficiency.
• Keep the MAP Sensor Clean: The LP5’s MAP sensor is known for clogging with soot, leading to incorrect fueling calculations. Cleaning it every oil change helps maintain proper air-fuel ratios.
• Monitor Your Injectors: The Denso injectors are strong but not invincible. If you notice rough idle or excessive smoke, get them tested before they fail.
• Inspect the Turbocharger Regularly: The BorgWarner VGT turbo on the LP5 is a strong unit, but carbon buildup on the vanes can cause slow spooling or boost issues. Occasional Italian tune-ups (hard pulls) can help keep the turbo clean.

Wrapping It Up: Easy Gains for Real-World Fuel Economy

You don’t have to sacrifice power to improve your LP5 Duramax’s efficiency. A few simple upgrades and smart driving habits can make a real difference—without turning your truck into a slug.

At Alligator Performance, we’ve got the right selection of performance parts and accessories designed to enhance your truck's efficiency and power. From high-quality cold air intakes and performance exhaust systems to advanced engine tuners and fuel additives, our products are tailored to help you sort out your LP5 Duramax or any other oil burner. Explore our extensive inventory and take the first step towards optimizing your truck's performance today.