I went over the power and ground connections, not expecting to find anything since they were not disturbed during the engine swap, all except the ground under the coils and the large stud at the passengers rear of the engine, behind the power steering pump on the non-s/c engine. I had to remove the alternator to get to that ground stud and while I could not easily move the connections on the stud, I was able to tighten the nut over half a turn. Maybe it will help?? No way to know for now. In any case, everything is clean and secure.
I have been making the assumption that the chip and/or interface device has been failing, so I tested that theory this morning. I installed the assembly that had run so poorly just a couple days ago into another ECM, which turned out to be my original one. The engine started, ran very briefly and quit. It did this five or six times in a row, then it started and continued to run on its own. It didn't sound very healthy with a seeming miss audible in the exhaust, but in less than a minute that cleared up and it settled down to a reasonable idle. I drove it a few miles and it doesn't miss a beat, but it has done this before. Why it had a hard time starting and running is a bit of a mystery. A flaw in the previous ECM being adjusted for in the Memcal or chip which came along for installation in a better ECM?? I just don't know. Of course, this begs the question of why installing a different Memcal in the previous ECM, twice, caused everything to return to a seeming normal. Maybe just doing a reset by removing battery ground and reconnecting would have done the same thing? Maybe tightening a harness ground to the engine helped? Only time and some miles will tell if this can be put to bed at last.