What is the best everyday tuner for a 2009 Duramax 6.6L for fuel mileage?

[5ToneRig_99]

With fuel prices where they are, I’m trying to optimize my daily commute and towing mileage. I know EFI Live with custom tuning (like DuramaxTuner or ATP) is highly recommended, but how does it honestly compare to box tuners like the Edge CTS3 or Banks Derringer for pure fuel economy?

What specific tune or HP level gave you the biggest MPG boost without sacrificing reliability? Are you running a clean "street" tune, or did you see better numbers after deleting the DPF?

 

[RustyF250_00]

Let's address the elephant in the room: if your 2009 LMM is still 100% emissions-compliant, your MPG is capped by the DPF. You can buy the fanciest tuner on earth, but every time the ECM triggers an active regeneration cycle to burn off soot, it literally dumps raw diesel into the exhaust stroke to heat up the filter. That single 30-minute regen vaporizes all the fuel savings you accumulated over the last two weeks.If you live in an area without visual smog testing and decide to go the fully off-road/weight-exempt route, deleting the DPF is where the real mileage is unlocked. On a stock emissions LMM, I averaged 14 MPG mixed. After removing the exhaust restriction and dropping in a clean, zero-smoke custom weight-optimized tune, my average instantly jumped to 18.5 MPG on the highway. The engine finally breathes, and the oil stays clean.

 

[Gooseneck_Gary]

For a 2009 LMM, EFI Live with custom tuning (from a reputable shop like DuramaxTuner) wins hands down over box tuners for pure fuel economy. Box tuners like the CTS3 or Derringer mostly manipulate rail pressure and timing globally, whereas EFI Live rewrites the ECM maps flawlessly to optimize injection timing for your specific setup.

Most guys see the best MPG gains on a clean 50–60 HP "Street/Tow" tune. Counterintuitively, a mild horsepower bump increases low-end torque, meaning your transmission shifts earlier and the engine doesn't work as hard to maintain highway speeds.

As for the DPF question: leaving it intact means you still waste fuel during regen cycles (usually every 300–400 miles). Dropping the DPF instantly nets a solid 1.5 to 3 MPG increase because you completely eliminate that exhaust restriction and raw fuel dumping. If you want maximum efficiency and reliability without smoking out the highway, a clean weight-fallback EFI Live tune is the way to go.