As Limu said, it’s a wiring addition to the truck. These old trucks aren’t ‘ready’ for a brake controller like a new truck would be so it’s a bit more involved. But the gist of it is the trailer has brakes on it. The truck has a controller. When you plug in a 7-pin connector vs a standard flat 4...
We might be closer to 2,200 fully loaded. I do have a v8 swap so there is plenty of power and the the OME heavy rear suspension also helps. I almost didn’t order the trailer with brakes but sure am glad I did as that makes a big difference. That is probably the biggest limiting factor