Backfire under load with an O2 error...where to start?

[Toronado3800]

My car has always thrown a slow response O2 code so I'm not real excited about starting there lol.

What is happening is I had a miss, could feel it at idle especially when it was warm, then finally when in overdrive trying to climb the long slow hills.  Finally I got the random misfire code and I went checking coil packs and plug wires.  One of the wires maybe lost connectivity when I was bending it around so I swapped it with an old one which did not.  All the coils are in range or at least where they were when I got them for the aftermarket one. 

Eventually the car has started to backfire under acceleration.  This happens most often climbing hills at partial throttle near 60mph or at 25ish when the tranny should really consider downshifting.

I bought a new coil and after rotating it in and test driving, on the 2nd try I changed one that actually has made a difference.  The car idles pretty well now.  It takes maybe a two minutes of sitting in gear to feel a miss and it does not have any pending codes.

Think my time is best spent with the O2 code, chasing down a vacuum leak (which I am BAD at finding) or fooling with more ignition components?

[RCA1186]

How are your plugs? My car will have a slight miss every couple of years that changing the plugs always gets rid of for me. AC-Delco or NGK plugs only, as these motors sometimes don't like the other ones.

[Toronado3800]

My plugs are a year or two old.  Can't remember which brand. 

I pulled the front ones in the fall when I did the wires and they looked so fine I put them back lol.  I guess changing them is something to do.

[Toronado3800]

RCA, you're gonna love it.

My MarkVIII had a coil over go bad on the way to work last week. I put a less bad one back on, then got a new one. It was the second coil over in a year so I decided to change the its plugs. Like the Aurora the MarkVIII plugs live in holes in the valve covers and besides having an inch or more of oil up to and on the boot they looked great.

SO,on a whim I ordered a set of AC Delco platinum plugs and Premium wires. Before I put wires on I always test them, I have gotten one bad one in the past.

The resistance on the longer ones were a bit high I thought, 21ohms ish vs ~6 on the shorter ones. Heck, the no name wires I was taking off were all 4 and 5's for resistance!

The old plugs looked fine except for having some oil on the boots. Something I did though fixed the miss and over 25 miles of driving no backfires. Could have been cleaning the plug holes out. Could have been the plugs, the new wires, cleaning that plate the coil packs sit on, who knows.

[RCA1186]

Well at least the miss is gone haha