As of November 2015, a replacement tailgate for a GMC Sierra can be purchased from CarParts.com, JCWhitney.com, PartsGeek.com, eBay.com and AutoPartsWarehouse.com. Replacement tailgates for a GMC Sierra are typically primed steel that can be painted and finished to match the truck.
There are different tailgate part specifications for different years and models of GMC Sierra trucks. The 1/2-ton, 3/4-ton and 1-ton models in any given year may have slightly different measurements for the tailgate. Automotive parts retailers such as JCWhitney.com, AutoPartsWarehouse.com and PartsGeek.com allow users to enter the year, make and model information to narrow search results to only those that apply to their vehicle.