2025 Denali Ultimate Duramax Specs. Select a sierra hd denali ultimate below to view specs. — 2025 gmc sierra 2500hd and 3500hd pickup trucks equipped with the denali ultimate trim are the only truck in gmc’s lineup that come standard with the 6.6l l5p duramax diesel engine, producing 470.
Adaptive cruise control with trailering assist, previously standard on the 2025 at4x and denali ultimate trim levels, now comes on the at4 and denali trims as well. 2025 denali ultimate is the most advanced and luxurious sierra ever.