Just wondering, when you replaced the wires before, did it get better?
Have you done the "total darkness test"? It may seem like a lame test but it does sometimes work with very dramatic results.
I have helped a few V6's with misfire problems. One in particular I remember that he reported changing the spark plug wires with improvement. Problem return some weeks later. After asking for a picture of the engine bay, the problem was instantly obvious. The spark plugs wires were not routed correctly and touching all sorts of metal parts. The insulation would hold for a short while but then break down. Guess what? The misfire would return.
Have you swapped the injector with another cylinder? I believe this test has been mentioned. For that mater, have you even inspected the injector electrical connector? What if moisture is present?
What is the condition of the spark plug when replaced?
What are the results of a compression test? Anytime a problem can't be resolved by the usual methods, sometimes it's not a bad idea to look at the health of the base engine.
2003 GT Convertible (sold & missed)
2000 GT coupe (Craigslist project. Fixed. Now my DD). Windsor to Romeo swap.