fairly sure i used copper but couldn't say 100% but i am pretty sure because i have already read up on how these engines don't like the platinum plugs. and i had the same #6 misfire code before i changed plugs and after i changed them it ran fine until now(around a month). Could a bad lower intake cause the P0300? the oil looks fine and so does the coolant. Maybe a bad plenium gasket? I just replaced the fuel pump about 5-6 months ago.