Well, I don't know if its physically doing anything to the vehicle, (IP or anything else), but it has made it quieter, and seems to be getting better fuel mileage. And I promise, I am not buying ULSD...remember it is not MANDATORY until 2010....Also, bear in mind I'm currently in a place where I could pull up to the Agricultural diesel pump and fill up w/ no questions, (if I wanted to do that)....I just bought the old 500ppm diesel on Sat....
