At first, reading your symptoms and actions, I thought it must be the injector wiring in the rotted harness shorting across the load (where the heavy leads are split out to the individual injectors) but then I read the result of your pressure gauge while driving test and I'm with the rest on vapor lock. Not fuel rail vapor lock necessarily, but vapor in the pump for lack of tank pump pressure.

This should be affected by the load of fuel (volume) such that it takes much longer to happen on a full tank than on a quarter. Having experienced the same symptoms with a tank pump running backward I would revisit the tank pump replacement. Make sure fuse 4 is supplying power to it. Perhaps in one of your three main pump swaps you ran the tank pump with the main pump disconnected for a volume test out the end of the 1/2" hose? About the only things that stop a Bosch main pump are lack of fuel input or lack of electricity input.
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Art Benstein near Baltimore

When everything's coming your way, you're in the wrong lane.