I have a 2001 gmc dually 3500............. message - misfire cylinder 6 after putting gas in from a station I do not usually fill at. Replaced plugs, wires #6 coil, injector, still getting same msg. rough idle, power loss, am noticing headlights dim when I accelerate at high speeds. Headlights have been doing that before the #6 problem. possible PCM problem???

 

Check compression first before thinking it's electronic related.