Fuel Pressure Drops after run

[nitrohydro2000]

I have a Holley Blue with the Reg set at 6psi. it is on a v6 Yamaha. It will pump fine for the first 30 min or so I run then it runs out of prime. I can't find any leaks or places it is sucking air. I have replaced the check valve at the tank , filters and still have the same problem. I just had this powerhead built and don't want to mess it up. The pump is only about a month old. Any advise would be appreciated.

[Euroski]

I removed the fuel tank check valve on my tanks. Also is the fuel pump mounted close to the same fuel level.

[nitrohydro2000]

It is mounted about 4 inches under where the problem starts I can only go about 2 inches lower before I'm on the floor.

Will it sypon without the check valve?