OK I run an 03 GMC 3500 6.0 ls2 4:10 gears 12 foot supreme box. At 225,000 I changed the plugs and wires. They looked fine coming out I put iridium plugs and msd 8mm wires on it. Before and after I changed them I had a slight misfire every once and a while only when it was idling. I figure its a...