Until you get it weighed with everything on board, you have no starting point. And remember, it isn’t how much you can carry/pull, it is how much can you STOP. Please check and verify your hitch, 5000# and 10000# are common, 8000# ? How many people are you talking about? Usual measure is 1500#/person, that gives you better safety margins. And that is just the ‘stuff’, not the weight of individuals included.
and no, you won’t be doing 70 down the road unless your goal is to stop at every truck stop in the country. 55 on hills, well people do have fantasies.