Wilbur:
Are you sure the rotors are warped. I'll have to look up the acceptable runout limit, but the only way to be sure would be to dismount the assembly and set them on a surface plate (on parallels because of the floating center) and gage them. Most every rotor is "warped" a little, even new and drums are out of round. That's manufacturing tolerances.
Interestingly, the acceptable out of round on a Meritor truck drum is 0.020 and they all seem to be close to that. Runout as well as out of round can and will be acerbated by how the bart is stored. Drums should always be stored open face down while brake discs shouls always be stored in a vertical position. The relentless pull of gravity warps them.
A little hint, when you need a grinding wheel for your bench grinder, always buy one that is stored vertically. grinding wheels stacked in a pile are no good. The close tolerance wheels for my surface grinder are all stored vertically, on a rack.