The HD (heavy-duty) label for Sierra signifies big trucks stretched to king-size dimensions. The series brings cabs of regular and extended lengths along with the four-door Crew Cab stocking car-like comforts. Muscular engines power these trucks to the top of the heavy-duty class, from a big-block 8.1-liter Vortec with 340 hp to a Duramax 6.6-liter turbo-diesel that musters 300 hp. In all, the collection includes 14 different models.
