I started having lack of braking issues on my 24' GN lately. So I checked the wiring and grounds, replaced my 14 yr. old controller with a Curt Tri-Flex and installed all new complete backing plates with little change in braking performance#@$%!. I have to turn the controller all the way up to have any noticeable braking, the wheels don't even lock up when empty on a grass pasture while applying the manual lever. Do the brake drums become slick(polished by shoes) over time and need to be turned, so they will grip better???. They are not warped, I previously only turned my vehicle hubs and rotors when they were damaged/warped by worn shoes/pads. Any thoughts???