Fuel pressure fluctuation

My fuel pressure keeps changing. I set it to 6 psi, then after it runs for a while the pressure drops to about 4. When I adjust it back up 6, it stays until I shut it down and let it cool down. When I start it cold, the pressure is up to about 9. I keep messing with it, but the pressure keeps dropping whenever it's fully warmed up. Any ideas?
Pump is a black electric carter, regulator is holley, press gauge is russel.