I have been going through the same thing with my 05. 3rd owner bought with 18k.
Drove my crazy...finally figured out #6 cylinder would foul over both plugs. I've swapped coils, injectors, put on new wires...For now I'll feed the habit. This winter I will also pull the valve cover and see what things look lie. I expect valve seals.
With new plugs the car rips up the road no misfires, etc..
Keep all posted last this winter.