2017-2019 GMC Duramax L5P Parts & Upgrades

How the L5P sits in a 2017-2019 Sierra HD

The L5P (RPO L5P, VIN eighth digit Y) arrived mid-generation. GM dropped it into the 2015-2019 K2XX HD body for 2017, which is why the catalog treats 2017-2019 as its own window. It is a 90-degree V8 with four valves per cylinder, 16.0:1 compression and a 1-2-7-8-4-5-6-3 firing order, built by DMAX in Moraine, Ohio, and it weighs roughly 835 lb. Air comes in two ways: the functional hood scoop with its 180-degree air/water separator supplies about 60 percent of it, the fender inlet the rest, through an A3231C panel filter and a plastic inlet tube that pinches down at the turbo. Fueling is Denso end to end, a factory electric lift pump through a frame-rail cartridge filter to an HP4 high-pressure pump, two rails at up to 29,000 psi and GS4 solenoid injectors that can fire up to seven times per cycle. The BorgWarner variable-geometry turbo lives in the valley between the heads, runs a billet compressor near a 61 mm inducer on journal bearings with its own oil supply line, makes around 28 psi, and does double duty as the exhaust brake. Behind it, the Allison 1000 (RPO MW7) runs 3.09/1.81/1.41/1.00/0.71/0.61 on DEXRON-VI. Other generations live on the Duramax hub.

What fails and why

On a Sierra that has worked, the front end usually speaks first. Steering wander and a dead zone where the wheel moves before the tires do are commonly reported on mid-to-high-mileage 2011-2019 HD trucks, along with idler and pitman arm play that clunks over bumps and weeping at the pitman shaft seal. Trucks that were leveled on torsion keys alone wear faster still, because the tie rod and CV angles get steeper and bring bump steer with them, and the IFS front end wears quicker than a solid axle once geometry is altered or power is added. Any pitman, idler or tie rod job needs an alignment behind it.

The Allison is the next limit. Add torque and the C3 clutch slips first; the 2011-and-later six-speed is good for roughly 500 rwhp before it does, and enough slip sets P0700 and locks the truck in third. Line pressure cruises near 80 psi and spikes to 220-230 psi on shifts, so heat is the thing that kills it, and the factory transmission-fluid thermal bypass valve can stick closed and keep fluid from ever reaching the cooler. Wheel hop is worth fixing for the same reason, since the Allison community blames it for P2 planetary damage on high-power trucks.

Sensor and heat items fill out the list. Carbon builds on the turbo's vanes and the vane-position sensor drifts, which shows up as surging, slow response and over or underboost codes, and it is worse on short-trip trucks. A thermostat stuck open runs the engine cold, the aftertreatment never reaches temperature, and DEF and NOx faults follow with poor economy. On the fuel side, contamination is the headline: water, poor diesel, or air drawn past a mis-installed filter O-ring causes more injector and pump trouble than anything in the design. Injector wear itself is uncommon and lands in the 150,000-250,000-mile range, usually traced back to fuel. HP4 pump failure is uncommon too and shows no strong mileage pattern, but debris travels, so the accepted repair is a complete OEM Denso package rather than a pump alone. Trucks that only run short trips can also dilute the oil with fuel, which reads as a level above full, foamy oil and a fuel smell on the dipstick.

Stock replacement vs. upgrade

Stay OEM-grade anywhere a sensor talks to the aftertreatment. ACDelco NOx sensors have the better track record on this platform than aftermarket units, a soot-loaded DPF is worth cleaning before replacing, and a damaged SCR catalyst wants the OEM part. The factory TP1015 fuel filter interval is 22,500 miles or two years; plenty of shops run it at 10,000 and so do we, because that filter is the cheapest injector insurance sold. On a short-trip Sierra, an oil catch can and a 5,000 to 7,500-mile oil interval are cheap answers to fuel dilution.

The upgrades that pay are the ones that fix a factory shortcut. Up front, a Stage 1-3 leveling kit with upper control arms keeps ball joint angles in range instead of leaving them hanging, forged steering assemblies and tie rods hold up on leveled or tow-heavy trucks, and traction bars take the hop out of the rear. For the transmission, a deep sump pan, an auxiliary cooler and PPE's billet thermal bypass valve 125065020 handle the heat; past about 500 rwhp the answer is a built unit with upgraded frictions, a billet C2 hub and a 4140 P2 planetary, which is what 750-plus rwhp trucks run. On airflow, PPE's 304 stainless turbo inlet kit 115020000 opens the pinched stock elbow, and Banks' 3.5-inch boost tube kit 25999 (CARB EO D-161-155) replaces the plastic charge pipes with aluminized tubes, five-ply silicone couplers and constant-tension clamps. Enclosed-box intakes from S&B and Wehrli keep the hood-scoop duct and its water separator path, but both are sold as 49-state, so tell us if you need a part with a CARB EO. A MAP relocation spacer (Banks 64410, listed 2017-2024) moves the sensor out of the EGR soot stream; its listing does not state CARB status, so confirm the EO before treating it as 50-state. If you tow heavy or run a tuned truck, an aftermarket lift pump and filtration system adds water separation and finer filtration ahead of the HP4, and the factory lift pump is widely called sub-par once power goes up. For the turbo itself, a reman or new OEM actuator is the normal repair, drop-in VGT upgrades keep the factory housing and actuator architecture, and fixed-geometry S400-class conversions are a custom-tune path that gives up the exhaust brake.

Tuning on a 2017-2019 truck starts from a locked ECM and TCM. A Banks Derringer 66652 (CARB EO D-161-149) is an OBD-II inline module with six levels, TransCommand and ActiveSafety that never reflashes the ECM, and a PedalMonster changes throttle response with no engine tune at all. Flash tuning needs an unlock first: the Edge Evolution CTS3 with Locksmith is rated Economy +75/150, Towing +100/200, Performance +125/250 and Extreme +150/350, requires every piece of factory emissions equipment present and functioning, and cannot ship to California. The unlock is permanent and tied to one VIN, and the Allison needs to be planned for alongside it.

What we carry

PPE carries the chassis and service side of this truck: forged 7/8-inch drilled steering assemblies, forged XR tie rod kits, the transmission thermal bypass valve, exhaust manifold-to-up-pipe gaskets, Micropure oil filters and heavy-duty differential covers for the rear axle. Wehrli Custom Fabrication fills in the fabricated hardware: Stage 2 high-flow intake bundles, 3.5-inch cold-side intercooler pipe kits, OEM/VGT turbo gasket kits, up-pipe bolt kits, thermostat housings and upper coolant pipes, transmission cooler bypass plugs and relocation brackets for a FASS system. Merchant Automotive is the sealing and gasket shelf, including the pass-through transmission connector seal that stops an Allison case leak and the HP4 pump installation gasket kit. MBRP covers DPF-back exhaust, mufflers and resonators, Mishimoto Performance Parts and BD Diesel cover cooling and driveline hardware, and BDS Suspension lists lift kits and heavy-duty tie rod kits for the 2011-2019 chassis. For towing there are B&W Trailer Hitches and Air Lift rear air springs for pin weight. FASS supplies water-separating filtration, Hot Shot's Secret and Lucas Oil cover engine oil and fuel additives, Alliant Power and XDP cover injection-side service parts, and Edge Products brings CTS3 monitors, EAS EGT and pressure sensor kits and A-pillar mounts. HP Tuners interfaces, a Calibrated Power Stealth Mach 1 turbo, Allison gaskets, a Mean Green high-output alternator, differential covers, fuel filters and the platform-specific tools are all on the shelf as well.

Fitment notes

Start with how your Sierra was built. Dual-tank and chassis-cab trucks are covered by fuel tank recalls 19V-088 and 23V-047, and single-tank pickups are not, so check before you order tank or line parts. Cab and box combinations were Regular Cab with the 8-foot box, Double Cab and Crew Cab with the 6.5-foot box, and Crew Cab with the 8-foot box; by 2019 the 2500HD Regular Cab came only in base trim 4x4 and the Double Cab only in base or SLE, which narrows what body parts apply. GMC made HID headlamps standard across Sierra HD trims for 2017, so do not assume a halogen housing, and lighting fits as a 2015-2019 HD range that shares nothing with the 1500 or the 2020-up T1XX trucks; factory bulb sizes are not confirmed, so verify by VIN. Factory wheels were 17x7.5 steel with LT245/75R17E on a base 2500HD and 18x8 steel with LT265/70R18E on a base 3500HD SRW, and 3500HD dually wheels do not interchange with single-rear-wheel wheels; confirm bolt pattern and center bore by VIN. Suspension is cataloged as one 2011-2019 range with separate 2WD and 4WD kits, and steering linkage spans the same years. The rear axle is the AAM 11.5 with factory 3.73 or 4.10 gears, even though some catalogs print it as an 11.8, so match covers and ring-and-pinion sets to 11.5. Monitor pods such as the Banks 63349 and 63350 are listed for 2015-2019 GM 2500/3500 because this is the K2XX interior. Turbo and actuator parts split 2017-2019, 2020-2023 and 2024-plus, actuator replacement needs a VATS recalibration with a GM MDI2 or the codes come back, and the 2024-up calibration tooling is different. Two diagnostic notes save money here: P1089 on an L5P is a fuel rail pressure code and not a boost problem, and the TCM is locked to the ECM on these years, so transmission tuning needs the unlock first. Brake rotors on 2018 regular-cab base-trim spec sheets measure roughly 13.8 to 14.0 inches front and 14.17 inches rear, DRW 3500HD rears may differ, and 2020-up trucks are a different application altogether.

Frequently asked questions

Why does my Sierra HD wander on the highway?

Worn steering linkage is the usual answer. Owners of mid-to-high-mileage 2011-2019 HD trucks commonly report wander and a dead zone at the wheel, and the parts behind it are the idler arm, pitman arm, center link and tie rods, or a worn recirculating-ball gear. A replacement gear cures it when the gear itself is the problem. Replacing the pitman needs a puller, and anything you touch in that linkage calls for an alignment afterward.

How much can a 2017-2019 Sierra HD actually pull?

A properly equipped 3500HD dually was rated up to 23,300 lb gooseneck or fifth-wheel with a 31,300-lb GCWR, and a 2500HD up to 18,100 lb on the 2018-2019 figures. Conventional bumper-pull is lower. Those are best-case numbers, and cab, drive, single or dual rear wheel and axle ratio all move them, so use the trailering label on your door jamb instead of the headline.

How much power can the Allison 1000 take behind an L5P?

Figure about 500 rwhp on a healthy stock unit. The C3 clutch is what slips first when torque goes up, and enough slip sets P0700 and drops the truck into third-gear limp. Line pressure matters as much as the clutch pack, since it cruises near 80 psi and spikes to 220-230 psi on shifts, and TCM pressure tuning has to match the build. Past that number you are into upgraded frictions, a billet C2 hub and a 4140 P2 planetary.

What oil and coolant does it take?

Ten quarts with the filter, SAE 15W-40 CJ-4 or CK-4 above 0 F or 5W-40 below it, on a 10,000-mile or oil-life-monitor interval, and 5,000 to 7,500 miles if the truck lives on short trips. Coolant is 50/50 DEX-COOL, roughly 31 quarts, so buy it by the gallon pair. A radiator drain only gets about 20 of those quarts, which is why a full job wants an evacuator or the block drains.

Which gauges work on a locked ECM?

All of the OBD-II ones, which is why monitors are the easy electronics upgrade on this truck. A Banks iDash DataMonster 66760 or iDash Pro 66710 and 66711 reads boost, EGT, transmission temperature, DPF soot level, regen status and DEF data over CAN without touching the ECM, and it pairs with a Derringer. Edge Insight and CTS-series units mount without drilling and read the same core data. Analog EGT gauges with a probe and a pillar mount are still an option.

Does my Sierra have an open recall I should check?

Three are worth looking up by VIN. Trucks with the optional engine block heater are covered by 19V-328 and 21V-496 for a cord and terminal short that can start a fire, and we would confirm that work was done before adding any electrical load at the cord. Dual-tank and chassis-cab trucks are covered by fuel tank recalls 19V-088 and 23V-047. A dealer can tell you in a minute whether any of them are still open.

Not sure what fits? Call the shop at the number in the header, or use the fitment checker on any product page. We install everything we sell.