that was typical of the early duraspark ignitions and a failure of the pick up coil inside the distributor when it got hot. SO it really does sound electrical. It could also have happened back when cars had only one coil, but your has 8 coils, one for each cylinder.
Does your check engine light come on? IF so it should be throwing a diagnostic code. Could be a bad ground to the PCM. If it is bad enough it should throw a code.
I just read in another thread that someone suggested getting a spray can of freeze or something like that, and that when the engine fails to spray components such as the computer, the coils etc. If they get cooled, and then the engine runs better, then you know which part/s need to be changed. I hadn't heard of this before, but wouldn't do it on expensive electrical components (like the computer) without expert advice.
You may want to speak to your mechanic about this idea. You may want to ask him how to test the computer next time you are sitting on the side of the road. | 
