2000 Mercury Marquis P0430 code

It started as codes p0305, p0307. Misfires on cylinders 5 and 7. I purchased new coil packs for the two cylinders and new plugs for all 8 and replaced them. Shortly after I noticed what seemed like a loss in power but much less than before. The problem quickly cleared up and check engine light remained off. Within a day or so the check engine light came on with the new code p0430. I feel the new code may be related to the previous problem. Maybe improper gaping on the plugs or faulty coil pack? Please help not sure what to do next and don't want to start replacing O2 sensors and catalytic converters unless necessary.