Do you have a fuel pressure gauge you can read from inside the car? Empty float bowl and symptoms sound like it is running out of fuel for lack of volume. Spend the money on a wide band O2 setup to get the mixture right and rethink the fuel pump situation. Never had anything but problems from the Holley pumps and regulators. Seen better results from a twin set of facets. The O2 sensor will let you see exactly what is happening when it stumbles.