Do I need a regulator?
Most o the Holley pumps require a regulator and a lot of the Holley regulators suck. I would remove the reg and verifiy system pressure. I set mine at 6.5 PSI. This is why I run Mallory pumps - the Mallory 110 in the Mustang is internally regulated at 7 and it's an install and run deal. We've had no issues with it, running a 400 HP 351C, shifting at 6000+ twice per pass. 3/8" stock line and stock pickup, large Fram filter.
I started with a system using a Holley 110 and a regulator and had similar problems. I did two things - 1) replaced the tank pickup with a 3/8 line and 2) sold all the Holley fuel stuff at a swap meet.
The Falcon runs a 140 GPH return system, it's good to near 600HP.
1967 Falcon 4 door 351C - 70 Mustang 351C
Owner built, owner abused.