Sponsored Links The new 2021 GMC Sierra is the third model year of the latest fourth-generation nameplate, arriving with a few changes and updates over the preceding 2020 model-year vehicle. Now, GM Authority has learned that new 2021 GMC Sierra 1500 orders in the Crew Cab Standard Box configuration are only available with 4WD. This is a significant change, and it’s uncertain at this time if the configuration restriction will be in place for the rest of the 2021 model year. Meanwhile, Regular Cab and Double Cab configurations of the 2021 GMC Sierra 1500 can be ordered with either 2WD or 4WD, as can Crew Cab Short Box configurations. However, Crew Cab Standard Box configurations are only available with 4WD.