We currently have an AC Delco R45TSX spark plug in our 454. The standard AC Delco is an R44T. At Autozone, they also offer a Denso Iridium, an AC Delco Rapidfire, and a Champion Double Platinum. Can anyone explain the difference in these, and what is the optimum plug for this engine? The 84 Blazer is a dd, but will do some muddin'. Thanks.