Go ahead and keep the truck & rv.
I have a 2004 ford f250 super duty diesel and a 2010 3670rl bighorn. Pulls it just fine and stops just fine. Braking will be fine, when you hit the brakes, the rv does not know if you have a 1/2, 3/4 or 1 ton truck, it only knows it has brakes and they are big enough from bighorn to stop it. Think about it, the rv stops itself, the truck stops itself in my opinion. Only problem i have is after a few hundred miles, the rv starts braking and wants to stop at the truck stop to buy more diesel, i can't break that habit!!
All truck companies have a safety factor built in to what they tell you, that you can pull.