How To Measure Fuel Volume.

PRH said
All that said, If your system is maintaining 6psi thru the finish line, it’s unlikely you have a fuel delivery issue.

This. Put a fuel gauge on it that you can read while driving.

If you have 3.5 psi at WOT and 0.120” dia. fuel inlet valves, you can support well over 500 hp.

Based on you et verses mph, you could have a fuel delivery problem, iMO.