So it's finally fixed, did 700+ miles yesterday and today and got the rig and myself home.
Theory as to why this was such a headache - the only real failure found was a bad fuel injector randomly finding ground through the case. (hot or cold, wet or dry, day or night, it didn't matter - it could show up at any time, and just as easily behave normally for a day and fool me into thinking I'd found the problem somewhere else).
My theory as to how that caused PCM failures is that the injector was randomly firing in response to the intermittent ground, building up an inductive voltage, and when a timed ground from the PCM was present it was grounding not only the 12v feed for the injector, but whatever induced voltage the injector had already built up.
Odd that it didn't blow the injector fuse, but two new injectors and an undamaged PCM and the rig ran as good as it ever has and did a few days of driving without a hiccup.
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