Turns out Transtar doesn't do bench tests. They sliced my old torque converter open and then told me what I already knew because after replacing it, I had the same set of symptoms. The TC was fine.

The problem was that the transmission fluid filter screen was clogged. I should have realized this from the symptoms - that it would work again for 5 minutes after sitting for a minute (because some of the crap fell off of the screen). Another clue I didn't fully utilize - the fluid level was high when the transmission wasn't working - because fluid wasn't being pumped (I was previously under the false impression that the TC was the only fluid pump in the system).
It could be that my first transmission problem was also due to this - which would mean I've only experienced one TC failure.

This time I put a couple of magnets in the pan before bolting it back on. I'll try to eventually post about how far I can drive with this transmission before it needs to be rebuilt.

John