First 5th Wheel--Bad Braking???

I find that it takes many miles for the burnishing to be complete. You might be finding an increase in performance for many hundreds of miles necessitating dialing back the controller repeatedly. Now the downside is that you and the repairman have worked the brake magnets to the extreme before they were seated, and that can groove the armature. I will never do the hard braking to burnish the brakes again, instead actually do with little braking for awhile.

Self adjusting brakes are far from perfect, the manual is just fine since the drums need to be pulled for brake inspection annually anyway.