Misfire in cylinder 8

[ndnwarpony]

Hello folks, I was wondering if I would be able to get some help from you guys. I have a 2000 Chevy Silverado 5.3 with 2 codes of a misfire in cylinger 8. The idle was rough after a quick drive and thats when all of this started. I replaced the spark plugs with Autolite Platinums about 2 months ago. I bought some new wires and swapped them out yesterday but that didn't fix the shudder problem. Could it be that the plug burned out or something? and where is cylinder 8 anyway? I still have the old plugs and was wondering if I could just find cylinder 8 then I could swap out an old plug just to see if thats the problem.