GVRW is a little misleading, as that figure is the tow vehicle, fuel, passengers, toys, and tongue weight....
And tongue weight is a combination what the manufacture figures what the frame can support (with the correctly matched hitch for said weight) -- ie, 250, 350, etc.
The towing weight (of 3500) is a manufacture 'recommended' max... it can't really be used when adding or subtracting numbers. One can ball park it, by taking GCRW, less curb weight, less max tongue weight = (your shite) & dry trailer weight --- regardless of the numbers, it's best to never get to close to MSR tow rating (of 3500). Sure the vehicle may pull it, but controlling it is another thing.
From experience, I know that no one really adds up the weight of all their shite correctly. Fuel, water, people, toys, and yes... even accessories (like the new bumper & winch that weights 200 lbs more than stock).
It's ALWAYS a good idea to load up with your normal weekend gear, pitch in the family, fill up the tank, grab some coffee, and hit the scales. At least you then KNOW your numbers.