Swapping coil packs is a very good suggestion.
You've changed out all the Fuel Injectors? Yes, new plugs definitely.
As well, you need to clean the connectors for the coils, the coil packs themselves and inspect the boots, if you have ignition cables from the coils to other plugs, I'd consider replacing them, they do NOT last the life of the vehicle.
Water or Dirt in the connectors to the coil pack can cause misfires, carbon tracking on the coil pack can cause shorting and misfires, bad boots or ignition cables the same.
Spraying electric cleaner or even brake cleaner, electric is better, into the connector and plug part of the coil. Scrub down the coil as well with the electric cleaner. I put dielectric grease on the connector to the coil packs as well the boots, it helps keep out the dirt and water and prevent the misfires.