Man and they sounded like they knew what they were talking about.
If you had an ice pack or anything that would keep it cool if you got a longer run time before the missing then that would indicate in my mind the PCM is the related issue. I had left for a while after starting this reply and after posting I see Dutch covered that point. It would be a no cost test just using ice. Before they pulled R-12 production computer techs could by spray cans of Freon. IBM must to have bought it by the box car load.
There is someone somewhere that is good at rebuilding them I am sure.
On the Ford F700 the starter is just find from late fall to early spring but in hot weather if we shut it off to get gas, etc it has to set 5 or more minutes depending on air temps before the dragging starter will cool enough to turn over the engine fast enough to start the engine.