[Cbrez]

Are you sure the rub marks are from your use? As you mentioned, perhaps it was from the previous owner overloading the rig. I would put some paint or tape on the rub spot and see if it is happening with the load you are Towing. Also seems like a payload issue if one side is rubbing and not the other. 4”-5” seems adequate if GVWR is not exceeded. A CAT scale should be in your future.