+1 on checking the wiring. I run a 2001 Trailswest 5 horse gooseneck.... well my wife does. I just get to fix it. Double check all wiring, grounds and connectors. A loose/corroded ground will cause a mess of problems that can be a pain to track down. We had ours rewired but still ran into inconstant brake performance. I cleaned up some connections in the junction box and cleaned the grounds at the junctions boxes between the wheels. It really helped but then I ran into more problems. I ripped each drum off and found 3 out of 4 brakes had the shoes delaminate completely. They looked to be original brakes, lots of friction material left its just that they let go. The friction material is bonded on to the backing. 4 new 7,000lb 12x2" Dexter backing plates were installed. Once they were adjusted and run in they seem to work great now.
Check the wiring and check the brake mechanicals!