it only happens when carrying a load
Rubbing in front or rear? I am assuming rear.
If it is the front though you can get some more room without cutting. Remove the bottom 2-3 flare fasteners that hold it to the fender, push the flare back and up a good inch, then refasten it with some stainless screws hidden inside the fender well. If it is still hitting the area right behind the flare is a sharp metal corner of the cab covered by black plastic. You can remove the plastic, grind down the metal, and put the plastic back on pushed further back so it never shows.