I have a 2005 C6500 Chevrolet with the 8.1 gas engine. The truck has been misfiring or missing more and more in the past month or so. Im going to do a tune up in the morning and see if I cant straighten it out. The problem is I paid a guy to do the plugs and wires before and He used 454 plugs in the engine and I'm not sure about the wires. It has been running fine but I would like to replace with original recommended plugs and wires. But I have nothing to go on anyone have a service manual or access to a database where I can find some part numbers. Our shops around here say " The computer says the biggest truck Chevrolet makes is a 3500. " I'm sure some of you have run into this before.