2000 GTP CEL showed misfire in cylinder #3. Plug had a crack in it so I replaced it, all good until a week later and the same problem, same cylinder again. Also have an O2 sensor code now. Could these be related? why would it only affect one cylinder? Maybe the coil pack? I'm goint to switch it with another and see if the problem follows. Any other ideas? Using Autolite XP iridium plugs