In the engineering world, you have to deal with "weakest link" technology. That means FOR YOUR SPECIFIC VEHICLE, you have to analyse the design and discover what the weakest link(s) is/are and make a plan to improve it/them. It could be brakes, cooling, suspension, tires/wheels, weight and balance, frame strength, power limitations, emission control, hitch capacity, durability, etc., etc., etc. Assuming you have a Ford product, the engineers at Ford generally don't like to help you because when/if they do, their neck is on the line should something go wrong. That's why they publish the specifications that they do, then shut up.
I know it's not the answer you want, but, the safest thing to do is buy the chassis with the performance you want, built in, and go from there. That said, there are thousands of people who will be more than happy to sell you something that helps you increase the towing capacity of your vehicle, but none of them will be around when/if you have problems. Or, if they are, they will point the finger at someone else. Your choice. Do you feel lucky?
Chum lee