Well there's only so much we can do online. Is it fairly common for a 'borderline' set of spark plug wires to act up as soon as the winter weather sets in? Probably yes. I see quite a few cars come in to the shop with rough running conditions as son as the winter sets in and it turns out they just need a tune-up. If you know the wires aren't 100%, I would say get rid of them anyway. How do you know for sure that it's only one cylinder missing and not different cylinders randomly missing? I had a miss one time that was driving me crazy. I would atart car, take off, then after driving for a while would just start bucking and missing. I was pretty sure it was a spark problem because it was a sharp miss as opposed to a 'bog' and as it got worse she would sometimes backfire out the exhaust which also lead me to believe she wasn't igniting the fuel consistantly and dumping raw fuel into the exhaust. Problem was my wires all seamed ok, plugs ok, and I just couldn't seam to trace it to any specific cylinder. It turned out to be the distributor. I replaced the distributor and she ran like a top. Now your distributor may be fine but the point is there are so many posible 'maybes' that we can guess at especially since your problem seams to be intermittant. Your just going to have to take some time and try and narrow things down. I would definately get rid of those wires either way. Have you checked to make sure your fuel pressure is within spec? There are so many 'basic' tests that would generally be done as soon as it came into the shop just to rule out certain things.
BUILT FORD TOUGH