Why is my spark plugs misfiring after tuneup? What else could it be?

Hi, This is a hard question to answer because there are many possibilities. The spark plugs are not the only reason a cylinder can misfire. There might be an issue with an ignition coil, fuel injector, or valve cover gasket. Sometimes the valve cover will leak oil into the spark plug hole. When there is enough oil, it can misfire. I would suggest bringing the vehicle to a shop that is more familiar with misfire diagnosis.