Ford Explorer cylinder 3 misfire

96 Ford Explorer (4WD); 120,000 miles--A while ago, the CEL came on and the code was for a misfire in two cylinders. I don't remember both cylinder numbers, but one of them was the #3. Ran fuel injector cleaner and replaced all spark plugs and plug wires. Ran fine for about 2 months, but CEL just came on again. This time, only one cylinder misfired and it was the #3 again. Since another cylinder misfired along with the #3 last time, it is difficult to say if the problem is specific only to #3 or if it just coincidence that #3 was involved both times. Engine does sometimes (not always) sputter and sometimes almost die upon starting it, but typically not noticeable problems once started. Something else that also may be a coincidence but the 2 times this happened happened to be the 2 hottest days of the summer--don't see how temp would affect a cold start, though. Also, it seems that this vehicle has always gotten poor fuel mileage (15-16 mpg with mostly highway miles). Have only had this vehicle for 9 months now, so not sure on past problems. Also, soon after buying, the O2 sensors crapped out--both were replaced along with catalytic converters under the dealership warranty since this happened within 30 days of purchase. Well, that is a ton of info--hope someone can decipher it. I have come across a ton of different potential causes, but don't know where to start and don't want to to trial-and-error if I don't have to. Leaning towards some type of EGR related problem so far, but I am obviously open to advice.