The GM brand makes the Sierra 1500, Sierra 2500HD, Sierra 3500HD, and the Canyon trucks. Each of these trucks varies in size from most minor to largest and has multiple different body styles, trim levels, and truck bed lengths. Unsurprisingly, the accessories made for each of these trucks are a different size and style.
For example, rear lights and the covers decorate rear lights to fit just the Sierra 3500HD, which won't do any other trucks. Step-up bumpers are made to fit the base model of the Canyon that won't do the base model of the Sierra. Suppose you want seat covers, floor protectors, tonneau covers, bed liners, retractable side steps, grip bars, or fenders of a different color or finish. In that case, all those accessories are available through the GM dealership near you.