Fuel pressure dropping while driving and under acceleration to zero at idle runs 4 lb electric Blue

I had a little bit of time to look at it. I took the pump apart and checked the screen. Everything looks fine in it. Put it back together. I set the fuel pressure at 5 and 1/2 and it stays at 5 and 1/2 island. But as the RPMs go up past 2000 idling the fuel pressure will drop. I'm not sure what that means it's a fuel lab pressure regulator set up for a return. I have 3/8 line before supply and return and 3/8 through the sending unit into the tank.