1999 Chrysler Sebring Misfire

Started misfiring approx 8 month ago. Finally threw a code "Cyl 6 misfire". Found corroded wire and terminal on cap. Replaced wire, cap, rotor. Had replaced this equipment at 110,000 when I replaced the platinum plugs. So at 130,000 after replacing again got alot better but still some small skipping. Mainly under load, going up hills, accelerating. Now has gotten progressivley worse. Threw another code yesterday "Misfiring on multiple cylinders". Checked the same #6 wire and cap recepticle - not corroded. Love the car, need to fix. One more note, did find a wire soldered to the #6 fuel injector wire - looks like car starter wire. Thoughts were coil, fuel filter, timing advance - really not sure?