When the L5P Duramax launched in 2017, it represented the biggest leap forward in Duramax diesel history.
Found in 2017–2019 Chevrolet Silverado 2500/3500 HD and GMC Sierra 2500/3500 HD trucks, the L5P introduced major mechanical and electronic changes that made it a powerhouse right out of the gate. These trucks remain one of the hottest options in the used diesel market today — combining modern performance, reliability, and style.
Whether you're shopping for one (or already own one), here’s everything you need to know about the 2017–2019 L5P Duramax:
Big Power from the Factory
The L5P introduced an all-new 6.6L Duramax V8 engine (RPO L5P), replacing the LML. GM didn’t just tweak a few parts — they redesigned the engine from the ground up.
Factory output jumped to 445 horsepower and 910 lb-ft of torque, making it the most powerful Duramax yet at the time.
Key engine highlights include:
- Stronger cast-iron block and rotating assembly — designed to handle higher cylinder pressures
- All-new Bosch high-pressure common rail fuel system with a Denso HP4 injection pump (replacing the CP4 found in LML)
- Bigger variable-geometry turbocharger with electronic actuator control for improved responsiveness
- New cylinder heads, pistons, rods, and crankshaft for improved durability and efficiency
The result? A stock L5P feels fast, smooth, and powerful — even by modern diesel standards.
Transmission: Allison 1000 6-Speed Automatic
The L5P was paired with the proven Allison 1000 6-speed automatic transmission. While it’s not the 10-speed found in later L5Ps (which has received mixed reviews), the Allison 1000 is well-known for its smooth shifting and solid reliability in stock and lightly modified trucks.
It handles factory torque without issue, and with tuning and supporting upgrades, it can reliably support moderate power increases. For extreme builds, aftermarket transmission upgrades are common.
ECM Encryption: The Biggest Tuning Challenge
One of the most talked-about features of the early L5P Duramax is the encrypted ECM. Starting in 2017, GM implemented advanced encryption that prevented tuners from directly modifying the stock ECM like they could with LML and earlier platforms.
This meant early tuners had to rely on ECM swaps—removing the factory ECM and replacing it with an unlocked unit to enable custom tuning. This added cost and complexity, but aftermarket companies eventually caught up with solutions through HP Tuners and other platforms.
Today, ECM tuning for 2017–2019 L5Ps is well established, but buyers should understand that tuning these trucks still involves more steps (and cost) than pre-2017 models.
Why the 2017–2019 L5P Is So Popular
These trucks hit a perfect sweet spot:
- Big power from the factory — no need for major mods to tow or daily drive confidently
- Modern styling & comfort — these trucks look sharp and feel refined inside
- Proven reliability — the L5P platform has a strong reputation for durability when maintained
- Growing aftermarket support — tuners, lift kits, fueling systems, and turbo upgrades are all widely available
For many enthusiasts, the 2017–2019 L5P represents the **best balance of modern performance and simplicity** before the 2020+ trucks added even more electronics and emissions complexity.
Common L5P Upgrades
Even though the L5P is strong from the factory, the aftermarket scene has exploded with popular upgrades to unlock more performance, reliability, and style:
- Aftermarket lift pumps & fuel filtration (e.g., FASS Fuel Systems) — improves injector life, protects the injection pump, and ensures consistent fuel delivery.
- Intake & exhaust upgrades — help the turbo breathe better and lower EGTs.
- Tuning — for owners looking to increase power beyond factory levels, tuning unlocks major performance potential.
- Suspension & leveling kits — give the truck a better stance and room for larger wheels and tires.
- Turbo upgrades — popular for enthusiasts chasing 650+ RWHP.
With proper upgrades and tuning, L5P Duramax trucks can comfortably make 550–650 RWHP while maintaining excellent street manners and towing capability.
Current Market Pricing (as of 2025)
The used truck market has remained strong, and **2017–2019 L5P Duramax trucks hold their value extremely well** thanks to their popularity and performance. While exact pricing depends on mileage, trim level, and condition, here’s a general breakdown:
- High-mileage work trucks (150k+ miles): $28,000–$38,000
- Well-kept mid-mileage trucks (75k–150k): $40,000–$55,000
- Low-mileage or pristine examples: $55,000–$70,000+
Special trims (Denali, High Country) and clean, lightly modified trucks often bring premium prices. Compared to newer L5Ps, the 2017–2019 models are often considered a smart buy due to lower complexity and proven reliability.
The Bottom Line
The 2017–2019 L5P Duramax trucks deliver serious power, modern comfort, and proven reliability — all wrapped in a package that’s aged extremely well.
Whether you’re towing, daily driving, or planning performance upgrades, these trucks are one of the best all-around diesel platforms on the market today.
FASS Motorsports: Your L5P Duramax Upgrade Experts
At FASS Motorsports in Washington, Missouri, we stock and install the most trusted parts for the L5P platform. From fuel systems and suspension kits to wheels, tires, lighting, and performance upgrades, our team can help you build your truck the right way.
👉 Shop L5P Duramax parts online
👉 Visit our Franklin County, MO showroom for expert installation & advice
Questions? We’re Here to Help.
- Phone: (636) 433-5410
- Email: info@fassmotorsports.com
FASS Motorsports
25 Town and Country Drive
Washington, MO 63090