GM's new 8.3-liter Duramax diesel for 2027 Chevrolet Silverado HD and GMC Sierra HD produces 555 horsepower and 1,230 lb-ft of torque, surpassing Ford's Power Stroke and Ram's Cummins on paper. However, raw engine numbers don't determine real-world towing capability, which depends on truck configuration, payload capacity, cooling, and braking systems. Full comparisons await pricing, fuel economy data, and long-term durability results when the trucks reach dealers in late 2026.