So, I checked the pump again. Nothing obvious wrong with it. While I was at it, I decided also I rewire the pump voltage supply wires through the service hatch. I used a ring terminal type bulkhead connectors with thick wires.

I observed a voltage drop only of 0.15 V at idle (pump terminals vs battery). Previously the drop was around 0.7 V and with all stock wiring it was much much more. I also blew compressed air through the fuel lines. Nothing came out and it seemed quite free flowing.

I put all together and went for a test drive. Did a couple of WOT pulls and according to the logs there is only about 20 kPA pressure drop now. Earlier I was seeing 40 to 50 kPA drop at WOT.

I wonder if pressure drop of this size is be expected with single in-tank pump and stock fuel lines. Regardless, I will be doing the fuel lines and hope to lessen the pressure drop even more. But right now I don't think the fuel pump is the culprit.