That's a good thought. I don't know if the O2 sensor can make that happen -- but it's certainly in the loop, so to speak.
Ranger coil packs have been known to have "issues" as well -- however, usually what you have is TWO cylinders that show misfires because each coil fires two cylinders.
All 3.0's DO idle rough -- some rougher than others. I'd tell you to clean your MAF; but you're getting misfire codes for a single cylinder? If you're getting them for two cylinders, and they are the "pair" that goes to a coil pack, you might want to look at the coil pack.
I just replaced my wires, a little after replacing my plugs and my idle DID get smoother, interestingly enough. My wires were 3+ years old, with 60,000 miles and a LOT of offroading water, dirt and mud having hit them.