Dump trailer rear(both) axle locks up.

Well after doing a complete brake job, s-cams,all bushings,drums, and replacing both brake valves. And 8 new tires(11r22.5). Everything is adjusted properly and working. But still the rear axle locks up coming to a stop. Yes i backed it off to 1 full turn. And still locks up.Trailer sits level front to back on tractor. Now I haven't weighed the rear axles individually yet. Going to do that shortly. Im assuming im really lite on the rear axle. Question is if I'm light on the rear axle could I put low-pros on to get more weight on rear of Trailer? Hence lowering the rear of the trailer? Or put lo pros on the front axle only?I believe I have the tallest 5th risers I can buy from holland for my truck. Needing advice don't won't to ruin 4 new rear tires. Thanks

 

I installed both new valves as well

 

Yeah good question I don't know how to get of hold of Benson. They don't make dump trailers anymore.

 

Well when I hook to a different trailer. No problems.
Dump is a 1996
Other trailer is a 2015

I'm curious if the wrong drums and shoes where put on at one time. And when I bought new the issue carried over?? I have noticed a gap between shoes and drums. I crank down on slack adjusters then back off 1/2 to 3/4. I only crank down until one shoe hits drum then back off. See pic