Fuel pressure ?

I'd try another fuel pressure guage first, I had a high flo mechanical that was starting at 10 psi cold and dropping to 7 hot which is normal when you consider what the spring against the pump diaphragm does, tension wise, as it warms up. My problem was to much pressure and needed a regulator, now it's 6.5 psi cold or hot. Even though your pump is new it might not be good. Have you checked your fuel filters also.

Terry