trailer brake problems

I recently bought a used tandem 10,000lb axle gooseneck trailer. The brakes were shot when I bought it so I replaced the brake assemble, didn't replace the drums. I am having problems with them working, they are adjusted properly. With my truck, I have a Prodigy P3 brake controller, I can just barely feel the brakes work when I hit the pedal, the controller is turned all the way up, if I hit the slide they will lock up. My cousin has a newer truck with a built in controller he used it...

trailer brake problems

trailer brake problems