There is a guy on here called "old used bear" that has helped me a number of times with mine. You can search under his name and get a lot of info, if that doesn't help you you can also email him. From your description it sounds like the green pressure switch, when they leak it does just what you are describing. Mine failed twice both times at low speeds. I now carry a spare of the green and gray switches. If you see any hydraulic fluid on the switch you know its bad. Unplug the wire harness from the end of the switch and look in there for fluid. The green pressure switch allows power to the pump to keep the brakes open when it fails the spring retracts and applies the brakes.
