I admit I'm a newbie who is just buying a 1st ever 5er, but I've been wrestling with the same issues so I'll give this a shot.
GVWR of the TV refers to the maximum allowable weight of the TV. That is dry weight plus everything you put in it-fuel, spouse, Doritos, etc. At 8700 you are under 10,000 so you are ok. When you have the 5er hooked on you add the pin weight. That leaves you 1300 for pin weight. Your 5er pin weight is probably 20-25% you projected actual weight of 14,800, or 2960 to 3700 of 14800. If you load 5er to max it will be 3020 to 3775. As I understand it you will be way over.
A trucks actual GVWR can be the sum of its axle/tire load ratings.
Example a F350 SRW can have a 7000 rawr and 5600 fawr = 12600 gvw.
Thats why the truck makers gvwr carries no legal meaning as far as how much load a particular truck may carry.
Ford markets the F350srw with a gvwr from 10000 lb up to 11500 lbs for the same exact truck. Just stay under any trucks axle/axle tire load ratings just to be safe.
Now if you choose to carry weight using the trucks gvwr that fine....its also safe to do so.
GCWR is the total allowable combined weight of the TV and 5er. At 8700 for TV that leaves you 14,800 for 5er. Again 15,100 is over unless you stay at 14,800 or less.
Another weight number that carries no legal meaning for roadside enforcement. There are no trucks on the road that carry a gcwr number on a certified placard nor is there a requirement for it.