Voltage Pulling Sierra

I am looking at purchasing a 2021 GMC Sierra 2500HD Denali (Black Diamond Edition). My dealership is telling me that the truck has a C7A code derated to 10,000 lbs or less. They say this is nothing more than a sticker allowing it to be used without a CDL and that the truck will still pull the 18,500 that the website says it will. I am trying to get an unbiased opinion. Looking to pull a camper with GVWR of 18K. The web showed it dropping a 5th wheel towing capacity down to 13,500 on a derated truck but if the motor, axles and suspension are the same, why would that be the case? Can anyone help?