They look to be normally erosion, although canÆt see the color of the base ring, but from the looks of the ground electrode, the heat discoloration band has move down past the radiusà most likely due to the heavy load of that beast you driveà could try one heat range cooler and see what the results are... typical with high energy ignition systems... as the plug center electrode wears from ionization, the gap increases... as the gap increases so does the voltage at the plug tip in order to jump the increasing gap... as the plug voltage rises, so it aggravates the erosion process by increasing the ionization at the center electrode... driving an engine hard also creates the same situation, higher cylinder internal pressure and temps expedite this process... typically a set of plug should last 25-30k miles, with the occasional re-gapping... both Denso and NGK make iridium spark plugs that will out last any STD plug 10:1... I prefer Denso to NGK, your callà they are a bit expensive @ $14 each.