GM’s heavy-duty trucks just got a new engine, a new steering rack, and a new brake system, all at once. The 2027 Chevrolet Silverado HD and GMC Sierra HD launch with GM’s first clean-sheet heavy-duty diesel in decades, a segment-first rack-and-pinion electric power steering system, and an electronic brake-boost architecture that replaces the shared hydraulic source that has underpinned HD trucks for years. Dealers are expected to receive the trucks beginning late 2026. GM has not announced pricing beyond a promise to share MSRPs in a future update.
The headline is the engine. The all-new 8.3L Duramax Turbo-Diesel V8, which GM previewed earlier this month under the Mongoose name, produces 555 hp and 1,230 lb-ft of torque, figures that are best-in-class among diesel HD trucks. The outgoing 6.6L Duramax diesel made 470 hp and 975 lb-ft. The 8.3L is built on a compacted graphite iron block with a fully forged crankshaft, connecting rods, and steel pistons. GM pairs it with a compact dual-stage air-to-water charge cooling system and a variable-geometry turbocharger, both tuned specifically for sustained towing loads rather than peak-output bursts.
The engine is assembled at GM’s expanded DMAX facility in Brookville, Ohio, a 1.4-million-square-foot plant that brings machining and assembly under one roof. GM had previously invested $920 million in that expansion to support the high-volume program. Both the new diesel and the updated 6.6L gas V8 are paired with Allison’s 10-speed 10L1000 transmission.
The gas engine is not a footnote. The enhanced 6.6L gas V8, assembled at GM’s Tonawanda Engine Plant in New York, now produces 412 hp and 472 lb-ft of torque, which GM says is best-in-class standard torque among all 2027-model-year HD gas engines. Updates include a new Turbo-Jet intake manifold, revised lubrication system, engine-mounted oil cooler, and a digital oil-level display. This is a different engine family from the Gen-6 Small Block V8 GM introduced for the 2027 Silverado 1500, which tops out at 481 hp in the 6.6L light-duty application; the HD 6.6L gas engine is its own architecture optimized for work-truck duty cycles.
Towing figures climb alongside the power numbers. Properly equipped diesel dually configurations can tow up to 38,000 pounds gooseneck and up to 20,000 pounds conventional. Every diesel dually in the lineup is rated for at least 30,000 pounds. Maximum GCWR reaches 46,500 pounds on select configurations. The 2024 Silverado 3500HD topped out at 36,000 pounds of towing capacity, so the new ceiling represents a meaningful step up for customers running commercial or agricultural trailers.
Steering is where the engineering story gets less expected. GM has moved the 2027 HD lineup to a rack-and-pinion electric power steering system, a configuration no other HD pickup currently offers. The outgoing hydraulic-assisted system shared its hydraulic source with the brakes; the new architecture separates those circuits entirely. GM says the EPS unit delivers approximately 30 percent more steering output than the previous hydraulic gear and can provide full assist regardless of engine speed or brake system demand. The practical benefit for work-truck operators is reduced kickback on rough roads and better on-center feel when towing, sensations that are easy to measure on a test drive and worth watching in first-drive reviews.
The brake system gets an equivalent modernization. Four-piston fixed front calipers clamp 14.6-inch front rotors, paired with upgraded rear hardware. The electronic brake-boost architecture replaces the hydraulic booster found in every other current HD pickup. Beyond stopping performance, the system supports Adaptive Cruise Control and Automatic Emergency Braking integration, and includes enhanced diagnostics for detecting brake fade or fluid leaks earlier than traditional systems allow.
Drive modes expand to match the new hardware. Normal, Tow/Haul, and Off-Road modes carry over with updated calibrations that coordinate the EPS, electronic brake boost, powertrain, and chassis as a single system rather than independent subsystems. New for 2027 on ZR2 and AT4X models is Terrain Mode, which enables one-pedal off-road driving in 4HI and 4LO: lift off the accelerator and the truck automatically applies braking to control descent speed on steep grades and technical obstacles. GM calls it a first for its HD lineup.
Trailering technology rounds out the capability story. Up to 14 camera views are available, including Transparent Trailer View, Bed View, and Surround Vision. The in-vehicle trailering app, Trailer Side Blind Zone Alert, and available trailer tire pressure and temperature monitoring are all carried over from the current generation with updated integration.
Silverado HD sales were up 12.4 percent to 47,099 units in Q1 2025, so GM is updating a lineup that’s already gaining ground. The 8.3L diesel, the EPS, and the electronic brake boost give the 2027 trucks a legitimate engineering story to tell. Not just a spec bump, but a ground-up rethink of three systems that buyers who actually tow for a living will feel every day.
