There is many many items that make up the vehicles GVWR numbers. The only way to know for positive is to sit down with a parts guy and start listing numbers for everything from the frame down to the ground.
I also think your looking backwards at the numbers. You actually have more cargo carrying capacity on paper than a 4X4. While it may have a 7200 GVWR, it also weighs 300 pounds more, so its cargo capacity is actually 100 pounds less. True cargo carrying capacity is... GVWR minus the trucks weight loaded ready to travel, Regardless of the marketing hype. Remember the numbers that the sales department cites is a bare bones truck with a 1/4 tank of fuel and one 150 pound driver. Everything you add above that subtracts from the real world net cargo carrying capacity. You really need to be concerned about that in BC, so load the truck up like you would go camping and hit the scales.