Low fuel pressure after making pass down track

I'm not sure this is the answer in your particular case, you may be dealing with a heat or othere issue
However it may be helpful in understanding how pressure regulation relates to flow into the bowls.
Often running lower pressure will result in steadier pressure during the actual run and better provide a better rate of flow.

Here's some info on the Mallory Pump
Holley/Demon Carb stumble

The experiment more or less starts here
Holley/Demon Carb stumble

read down for his test results