Did it blow a chunk out with it? I have the kit that has a reamer, and tap and the big ass insert that you screw in and then screw in the factory plug.. this..
I get half the mpg with my 6.7 towing than I did with ole whitey.. At any speed or load! I get the same mpg unloaded at 80mph... only thing the 6.7 does is better at 56mph...
I'd put my old dually up against my 15 6.7 to 80mph any day