The 2018 Chevrolet Silverado 3500HD is available in four trims: WT, LT, LTZ, and High Country. On the WT and LT trims, you can choose from Regular Cab, Crew Cab, and Double Cab body styles. The LTZ is available with the Double and Crew Cab body styles, while the High Country is only available as a Crew Cab. You can also choose between two box lengths: Standard and Long. However, if you opt for a Regular or Double Cab, those body styles can only be paired to a Long Box.