Best Tuners For 6.6L LLY Duramax (2004.5 – 2005)

| Last Updated: December 24, 2021

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GM’s old 6.6L LLY Duramax engines are some of the most reliable models out there – but let’s face it, at this point, they are getting pretty old. Instead of sinking a lot of money into high cost repairs, or even an entirely new truck, have you ever considered revitalizing your truck with a tuner?

Read on to learn about the many ways a tuner can wake your truck’s engine right up!

Comparison of the Best 6.6L LLY Duramax Tuners (2004.5 – 2005)

  • Has a five inch screen with full color
  • Boosts both torque and horse power for your engine
  • Comes with four settings: economy, tow, race, and extreme
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  • Produces tangible power gains that are still safe
  • Great for evening out a truck’s torque and speed
  • Good at maintaining power even while going uphill
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  • Fixes any “check engine” light problems that may pop up
  • Bumps up gas mileage by 20% or more
  • Enhances both throttle response and shifting for your engine
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  • Increases miles per gallon by up to three miles
  • Will make your truck run efficiently when towing
  • Tunes will upload quickly, within ten minutes or less
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What Years Fall Under 6.6L LLY Duramax?

If your truck is rocking a 6.6L LLY Duramax engine, you are one of the few. GM was producing trucks with these engines for a very limited period of time, so when looking into finding a tuner for your truck, you are going to want to be conscientious and make sure that whatever tuner you choose will be compatible with your truck’s engine, since not all of them will be for such a niche market.

GM was producing 6.6L LLY Durmax engines for just a year and a half, from midway through 2004 to 2005. If your truck falls under those model years, this article is for you.

What You Can Expect After Installation

When you have installed a tuner, you can expect to see the following changes:

Fuel Economy

The one bad thing about driving a truck is that it will eat up your gas budget pretty quickly. Tuners can change all of that forever by boosting your truck’s fuel efficiency and increasing it by several miles per gallon, at least.

Improved Power

Many people who install tuners on their trucks use the phrase “waking up” to describe how their trucks behave post installation. It can be pretty incredible what you discover your truck is capable of doing after it is jolted awake by a tuner!

Enhanced Shifting

All trucks struggle with one fatal flaw – the tendency to randomly downshift when going up hills. Say goodbye to that hindrance forever after you have installed a tuner! You will be able to maintain your speed going uphill with ease.

Review of the Best 6.6L LLY Duramax Tuners

Now that you know a bit more about what tuners can do for your trucks, here’s a list of the best products available on the market today:

Best Overall 6.6L LLY Duramax Tuner:
Edge Evolution CTS3


  • Increases efficiency when towing
  • Built in “Mileage Coach” will enhance fuel efficiency
  • Improves both torque and horse power on your vehicle
  • Has option to switch between different measurement units
  • Comes with four different settings: economy, tow, race, and extreme


  • Can be hard to switch truck to Economy setting

The Edge Evolution CTS3 Tuner is the tuner on the market that provides the most incredible user customization experience. If it is important to you to invest in a tuner that will not only improve numerous aspects of your truck, but also be fully individualized, this tuner is the one for you!

Its five inch, full color screen allows users to choose which colors will specifically coordinate to which measurement of your truck’s vitals, so you will be able to keep track of exactly what is going on with your car with just a glance at the screen.

The Evolution also gives you the option of many different screen backgrounds and a big range of different screen layout styles as well. It is so customizable, you can even switch between units of measurements, whether you want U.S. units or the metric system.

And perhaps best of all, the built in “Mileage Coach” on this tuner will work to maximize your engine’s fuel efficiency through miles per gallon calculation, trip monitoring, and constant fuel saving tips.

Bottom Line

If you are looking for a fully customized tuning experience, look no further that the Edge Evolution CTS3 Tuner. Keep in mind that not all settings are super easy to access, though.

Bully Dog GT Platinum Diesel Tuner


  • Versatile
  • Lightweight
  • Easy to install
  • Delivers strong (but safe!) gains in power
  • Bully Dog provides good customer service


  • Tuner needs to be activated by Bully Dog upon arrival

The Bully Dog GT Platinum Diesel Tuner is an incredible tuner that will connect directly to your LLY Duramax engine’s unlock cable, enabling you to unleash your truck’s full power. This maximized power will noticeably improve many aspects of your truck’s performance.

Instead of constantly struggling with unwanted down shifts when your truck is going up hills, you will be able to maintain your ideal speed. The speed and torque on your vehicle will balance out. And all that with an additional miles per gallon increase: some users have reported that the Bully Dog GT was able to boost their miles per gallon by up to four miles!

If you are shelling at the cost of a tuner, that fact alone should be enough to convince you to invest in one – we all know trucks are not the most fuel efficient vehicles on the market, and the Bully Dog GT will rapidly pay for itself in conserved fuel costs

Bottom Line

The Bully Dog GT Platinum Diesel Tuner is an awesome tuner that will enhance pretty much everything you could ever want improved about your truck. Just know that you will need to take a second when it first arrives to call Bully Dog and get your tuner up and running.

3. EFILive AutoCal Tuner


  • Versatile
  • Durable
  • Easy to use
  • Lightweight
  • EFILive provides good customer service


  • Instructions are not particularly thorough
  • Does not come with a storage or carrying case

The EFILive AutoCal Tuner is a great tuner that will improve productivity and overall efficiency on multiple different areas of your truck, but most prominently when it comes to gas mileage. Wait for it – users report that when rocking the EFILive AutoCal on their trucks, they are able to save up to 20% in fuel costs, with how much this tuner is able to bump up their miles per gallon, even on lengthy trips.

Plus, the tuner will also improve truck shifting and auto response, so there is really not anything to complain about with the EFILive AutoCal And say goodbye forever to struggling with constant “check engine” lights popping on – this tuner will immediately address that issue. All that plus enhanced power? You are going to want to rush out and get yourself an EFILive AutoCal as soon as possible!

Bottom Line

The EFILive AutoCal Tuner is a wonderful tuner that will enhance your truck’s throttle response, shifting, gas mileage, and of course, overall power capabilities. The only thing to potentially consider with this tuner is that it may take you a little while to set it up because the instructions are not the most helpful.

4. PPE Standard Xcelerator


  • User friendly
  • Easy to install
  • Reliable and safe
  • PPE provides good customer service
  • Addresses speedometer issues if you have made any modifications


  • Potentially will increase your truck’s exhaust emissions
  • Does not have the option to program on the fly as it requires fuse adjusting to change tunes

The PPE Standard Xcelerator is an excellent tuner that will enhance basically everything about your truck’s engine. If you are aiming for increased fuel efficiency, this tuner has got you covered: users report that they are able to increase their miles per gallon by at least three miles, with the chance to increase by even more when you are the highway. It will also improve your truck’s towing capacity, no matter how heavy the load.

When adjusting tune settings, this tuner is quick and efficient, meaning you will not be wasting time waiting for your tunes to upload instead of out maximizing your truck’s power boosts. Plus, it will make your truck’s shifting smoother, so you will no longer have the annoyance of your truck randomly downshifting when you are going uphill.

Bottom Line

The PPE Standard Xcelerator is a top notch tuner that will make every aspect of your truck a million times better, to sum it up. But keep in mind that the boosted power this tuner gives your truck will also lead to an increase in smog emitted.

5. DiabloSport Predator 2 Programmer


  • Simple to use
  • Updates itself quickly
  • Has great instructions
  • Quickly uploads different tunes
  • Easily adjusts based on tire size


  • Does not have a mount to attach to dashboard
  • Diablo Sport does not provide good customer service

The Diablo Sport Predator 2 Programmer is a great programmer that will cause a number of measurable improvements in your truck’s functioning. The most noticeable will be your increased fuel efficiency – users report that the Predator 2 can boost their miles per gallon by 10% to 20%! That alone will make this tuner pay for itself in no time.

But that is not all the Predator 2 can do for you – when you move from the Eco tune to the Diablo tune, your truck’s horse power will also increase by 10 to 20!

And say goodbye to shifting woes – this tuner will clean those right up for you as well. If you have made any modifications to your truck, the Predator 2 can align your speedometer to your truck’s new mods, including an automatic calibration feature based on tire size.

Bottom Line

The Diablo Sport Predator 2 Programmer is a great tuner that will make a tangible impact on multiple different aspects of your truck’s operation. It does not come with its own mounting mechanism, so it may be a little complicated to install, though.

How to Choose an LLY Duramax Tuner

Now that you have a bit more familiarity with the products, here are some important things to consider when making your final decision:


High quality tuners will improve basically everything about your truck, beyond just enhanced power and fuel economy. And increased efficiency means better, smoother operation, which will ultimately result in far fewer dollars spent on costly repairs.

DiabloSport Predator 2 Programmer

Vitals Monitoring

The best tuners will not only improve your truck, but also report on exactly what they are improving and how, so you will know exactly what is going on with your engine at all times. Forget freaking out when your “check engine” light comes on – odds are, you will probably already be expecting any issues with a good tuner!

Ease of Use

Taking on any sort of do-it-yourself project with your truck can be pretty intimidating, so the last thing you want is a tuner that is incredibly complicated and difficult for someone unfamiliar with a tuning system to use. Find a tuner that will make your life easier, not more stressful.


Tuners will change the game for your truck, taking a tired old 6.6L LLY Duramax engine and making it feel like brand new again. Think about what exactly you will want a tuner to do for your engine and then reap the benefits! We guarantee you will not be able to go wrong with any of the tuners here on our list. 

Sean comes from the forums actually and drives an OBS Ford. He writes fantastic DIYs and knows his way around a camera, too. We keep him caffeinated and away from DPF filters to avoid another rant about recent emissions restrictions.