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.
I found my problem with code#2 was that tank had pinched MAP sensor hose. Whoever installed it last had rushed and just slapped tank on without using another hand to hold hose to side. In your cleaning of tank, you most likely released pinched hose when removing and was careful not to pinch it when re-installing.
I initially tracked that down by measuring MAP-sensor output voltage according to manual. There was slight discrepancy between my readings and manual's numbers along with a time-delay in response to throttle changes. My 1st intent was to remove MAP sensor for bench-testing and cleaning if needed. That's when I found pinched hose.
Manual's test section for all these codes have been spot-on for resolving issues.