So I dug into this more today. It was low on fluid so I bled the system but that didn't solve the problem. I tried adjusting the brakes with the starwheel (they are drum brakes) but it never got tight enough, even when adjusted all the way.
It seems like it has no brakes until you push hard enough on the tow vehicle brakes then it locks up. It releases when not on the brakes, but skids the tires with any moderate braking action.
I guess next step is to pull the drums off and see what's going on inside