Well, it turns out my "new" (remanufactured) Bosch starter is dodgy. Tried jumping battery (+) directly to the solenoid trigger terminal -- still nothing, not even a click.
Took out the starter, bench-tested it again just to be sure, still nothing. Then I turned the pinion gear a bit by hand and tested again; suddenly it woke up. Gave it several more tries, still responding, so I reinstalled it.
Once back in the truck, tested starting and got one good crank out of it, then dead again. So I'll pull it yet again tomorrow, and back to RockAuto it goes...
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