The trucks and SUVs made by Chevrolet and GMC are almost identical. GMC vehicles, however, cost more than Chevrolet vehicles because General Motors markets GMC vehicles as more professional and upscale.
The two different brands use the same engines, parts and other materials but may have slightly different styling cues or trims. Some people prefer GMC vehicles for those or other reasons, but more people choose to buy Chevrolet vehicles than GMC because of the price difference. Perhaps the prices of GMC trucks and SUVs are higher on the used vehicle market than similar Chevrolet vehicles because fewer GMC vehicles are sold.