How long since last bearing repack? If it has been more than two years it is defiantly time for a repack and brake inspection.
I have a Prodigy P3 and a year ago I had a similar braking problem. When I checked the current draw I found the current was low for the voltage applied. With a four wheel trailer the current will be about one amp per volt applied.
I found a bent connector in the 7 way. Replaced the connector and problem solved. This is the reason I chose the Prodigy P3 controller. Best diagnostics on the market.