With regards to payload and fuel, with Ford, you do not need to subtract fuel weight from your available payload.
Ford defines payload as GVWR - base curb weight. And base curb weight is defined as "weight of vehicle including a full tank of fuel and all standard equipment". The 2015 Towing Guide referenced earlier states this as does the 2014 Towing Guide I have saved.
I cant speak for how other manufacturers calculate their payload but Ram's web site also says that curb weight is with full fuel and all other fluids full.