I am assuming this is the ONLY DTC code. If so, it is unlikely to be a bad coil pack. Why? Because cylinder #5 would be affected as well.
Have the alternator tested for excessive AC ripple. Autoparts store will test for free.
OP states new plugs and wires. How about the routing of the wires? Did you follow factory routing? Use all looms and standoffs?
Try this old racers trick. Run the car in a totally dark location. Look for the blue hue of arcing.
As for other things that could affect a single cylinder, a bad fuel injector or base engine problem (value/low compression).
This could also be a cam sensor problem.
If the car immediately improved after replacing the plugs and wires and then started acting up again, my vote is acring caused by incorrect spark plug wire routing.
2003 GT Convertible (sold & missed)
2000 GT coupe (Craigslist project. Fixed. Now my DD). Windsor to Romeo swap.