The L5P is the current 6.6L Duramax, used in Silverado and Sierra heavy-duty pickups since the 2017 model year and identified by an 8th VIN digit of Y. It was rated 445 hp and 910 lb-ft through 2023 and 470 hp and 975 lb-ft from 2024. The Allison 10-speed replaced the six-speed for 2020.
GM called the L5P an all-new Duramax when it launched for 2017. It uses a stronger heat-treated cast-iron block, revised aluminum heads, a Denso HP4 high-pressure pump with Denso solenoid injectors in place of the LML's Bosch CP4.2 and piezo injectors, an electronically actuated BorgWarner variable-geometry turbo, and a functional hood-scoop air intake. Emissions hardware includes EGR, an oxidation catalyst, a DPF and SCR with DEF.
For 2020, the redesigned Silverado and Sierra HD paired the L5P with the Allison 10L1000 10-speed automatic. The 2024 update added a new turbocharger and actuator, tapered-bowl pistons, higher-pressure injectors and stronger rails, and revised head cooling, raising output to 470 hp and 975 lb-ft. Most owner-facing issues so far involve emissions sensors and DEF components rather than the core engine.