Okay, I finally had a little time to look into my rubbing issue. I thought it was my mud flaps but the tires aren't actually touching them. A couple months ago I installed a drain hose for the AC condensate drain in the firewall, to keep it from draining onto the frame rail. I routed this to the outside of the frame rail, but it was too far back on the rail. The stock tires must have barely cleared this hose but the AT tires I installed were just big enough to make contact. Re-routed the hose and no more rubbing. Sorry for the misinformation.