There have been several posts regarding springs getting weaker but few, if any, reports of tires rubbing. Are your's rubbing all the time or are there just signs of them rubbing on the area over the tires. What is the distance from the top of the tire to the bottom or the slide floor when parked?
Another question is regarding weight. Have you weighed your rig? You might be well advised to go to a good spring shop for an inspection of your suspension.