2021 GMC Sierra 2500HD 6.6L L5P Duramax Turbo Diesel Engine & Allison 10-Speed Transmission Complete Dropout Swap (18,000 Miles)

2021 GMC Sierra 2500HD 6.6L L5P Duramax Turbo Diesel Engine & Allison 10-Speed Transmission Complete Dropout Swap (18,000 Miles)

Looking for the ultimate, heavy-duty powertrain replacement or custom conversion package for your rig? This ultra-low-mileage 2021 GMC Sierra 2500HD 6.6L L5P Duramax Turbo Diesel engine and Allison 10-speed automatic transmission complete dropout swap is the gold standard of modern pulling power.

With only 18,000 original miles on the odometer, this late-model, turn-key powertrain offers an incredible opportunity to secure a factory-fresh diesel platform. The L5P generation Duramax represents the pinnacle of GM diesel engineering, delivering a massive factory-certified 445 horsepower and 910 lb-ft of torque. It is highly sought after by contractors, hotshot haulers, farmers, and heavy-duty 4×4 builders across both the American and Australian markets for its relentless torque, upgraded thermal efficiency, and unbreakable drivetrain components.

Technical Specifications & Features

GM 6.0L / 6.6L L5P Duramax Turbo Diesel V8

• Engine Family: GM Duratec / Duramax Diesel V8 (Gen 5 Architecture)

• Displacement: 6.6 Liters / 403 c.i.d.

• Performance Output: 445 HP @ 2,800 RPM / 910 lb-ft of Torque @ 1,600 RPM

• Engine Block & Structural Integrity: Deep-skirt cast iron engine block featuring induction-hardened cylinder bores, robust 4-bolt main caps, and a forged steel crankshaft for maximum durability under extreme load.

• Fuel Injection System: Advanced 2,500-bar (36,000 psi) Denso common-rail direct injection system, paired with electronic solenoid injectors for near-instantaneous throttle response and quiet, clean combustion.

• Aspiration: High-performance variable geometry turbocharger (VGT) featuring an integrated electronic actuator to supply linear, lag-free boost pressure across the entire RPM powerband.

Allison 10-Speed Automatic Transmission

• Gear Ratio Architecture: Legendary Allison 10-speed transmission layout featuring ultra-tight gear-ratio splits to permanently keep the L5P engine directly in its peak torque sweet spot.

• Heavy-Duty Internals: Upgraded with robust torque converters, heavy-duty clutch packs, and a strengthened case designed specifically to withstand nearly 1,000 lb-ft of continuous torque without overheating or slipping.

The Ultimate Heavy-Duty Towing & Conversion Platform

• Engineered for Extreme Loads: Whether you are towing heavy commercial trailers, hauling agricultural machinery, or building an elite overland custom rig, this powertrain combination handles sustained, high-load driving with effortless ease.

• Next-Gen Factory Improvements: The L5P features major factory upgrades over older diesel generations (like the LML), including a significantly stronger engine block cast, high-flow cylinder heads, an electronically controlled oil pump, and an integrated oil cooler.

• Unrivaled Low-Mileage Quality: Finding a pristine, running L5P package with under 20k miles is an absolute rarity. Every internal bearing, seal, and fuel component is essentially in factory-fresh mechanical condition.

What’s Included & Logistics

This premium heavy-duty diesel pullout package has been thoroughly multi-point inspected, computer diagnostic scanned, and run-verified to guarantee absolute mechanical and electronic operational health.

Package Includes: Complete 6.6L L5P Duramax engine assembly (oil pan to intake), factory variable geometry turbocharger, full fuel injection system, common rails, individual glow plugs, all front engine accessories (high-output alternator, power steering pump, water pump, brackets), engine wiring harness, factory engine management module, and the matching Allison 10-speed automatic transmission with torque converter safely seated.

Due to the extreme weight and commercial footprint of this diesel powertrain setup, it is strictly bolted to a heavy-duty pallet enclosure and shipped via fully insured freight transport across the United States or prepared for direct containerized ocean freight routing to major Australian shipping hubs. Contact our team today with your zip or postal code for a fast, competitive shipping quote!