Some of the GM/Chevy trucks have a front end designed to support the weight of a snow plow. At one point it was an option and later it was standard and for 2015 who knows?
The front suspension also bears the added 800 lb. weight of a diesel engine if that is used with the truck. But the trailer weight if anything reduces the weight on the front wheels (if the rear sags too much) but certainly does not add to the load at the front so you can ignore the front and pay attention to the back.
Again, the factory calculations are based on the weakest link when the truck left the factory. You can easily upgrade that weak link which will be the leaf springs or the rims and tires by adding to the leaf pack or adding overload springs or air bags or replacing the rims and or the tires.
The GCWR, which factors in the frame and overall suspension and engine and transmission and drivetrain components, is the one number that cannot be changed for a vehicle. I want to keep the total weight of my truck and its payload and the trailer load well under that amount.