Routing fuel lines correctly

I have the stock fuel filter with 5/16 inlets and a 90 degree 1/4 return outlet. I was trying to find one with threaded inlets to reduce the amount of rubber hose and hoseclamp connections and have since put that on hold. What I am curious about now is the effect of running a 5/16 line into a 3/8. My guage is reading 4 psi and drops to 3 psi at partial throttle. It is my understanding that it should increase with rpms not the opposite. First the guage was bouncing drastically and a fuel filter replacement fixed that issue. Next i replaced the new fuel pump with another know working pump, but I still cant seem to get anything past 4 psi even with the regulator bypassed 5/16 line all the way to the carb . It sits at 4 psi and then drops with throttle. Any thoughts on what could be causing this? No leaks in the lines up front I will check the hard line to tank hoses today.