Holley/Demon Carb stumble

With regards to operating pressure.

One potential problem running “higher” pressures is if the system is unable to maintain the set pressure for the entire pass.
If the pressure steadily drops throughout the run, so does the float level.

So, if you set the pressure at 9psi, you have to have enough fuel pump/system to be able to maintain it.
If you can only maintain say, 6psi at the top end...... you’d be better off setting the pressure at 5psi, so it would be the same for the whole pass.