'97 TBird misses and then smoothes?

My '97 TBird (4.6 L V-8 w auto and ac, 157 k) Runs really great, as I have owned and maintained it well since 1998. Lately, however, it does a curious thing. If I drive long enough each day when I first start it(at least 4-5 miles continuously)it will produce a brief miss right when the temp gauges indicates fully warmed up (it always rides just below 1/2 to right on half-way). This lasts anywhere from 5-10 seconds; usually only 4 or 5. Then it smoothes out and won't repeat for the rest of the day! If my first trip is too short to allow it to fully warm up (anywhere from 1-3miles), it will never have the miss? I have learned to relax because it always smoothes out, but is it trying to tell me something is about to fail? CEL is not on, and I don't have an OBD code scanner, which I have been told wouldn't produce any code anyway w/o The CEL being on. Surely someone has just the right slant on this and I await the help of one and all. Thanks, maybe I can answer someone else's question someday.