If you have both set at MAX and still have poor braking you have a problem somewhere.
Jack up one side of the trailer and while spinning a wheel have someone hit the manual control. That should SLAM the wheel to a stop. If you do not get this reaction from each wheel its time to start some deeper investigation.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles