[ChuckS]

I do not believe the issue is with your Trucks integrated brake control ..

All four RV brakes are wired in parallel.. The signal that is sent to one brake manet is the same as the other 3.. ( voltage and amp )..

I would pull that hub back off and check:
1. Measure the resistance of that brake magnet ( 3.2 ohms ) typical
2. Use a straight edge and measure across the magnet surface for overall flatness of the magnet face
3. Check the two wires leading into the coil on the magnet for any evidence of damage, looseness, etc
4. Check the operation of the self adjust mechanism on that brake ( the brakes adjust themselves Only when brakes are applied and moving forward)