Closing the loop on this:
I tested the fuel pump for both flow and pressure and everything checked out okay (above the minimums in the manual). The flow rate was almost 2x the specified minimum. Pressure was right at 50 psi.
Removed the pump from tank to inspect. Tank was relatively clean and free of corrosion. Pump inlet filter was very dirty and there was "a lot" of particulate contamination around the outside and underneath the filter. It looked like sand.
I decided to just put in a new pump (+filter, seals, pressure regulator, etc) since I had everything apart.
Took it to the track yesterday and the issue appears to be resolved. It's great news but kind of unsatisfying to not find a specific cause for the problem. The only theory I have is that somewhere on the old pump's curve, the flow drops off enough to trigger the fault.
B.