3/8 vs 5/16 fuel lines

I'm running a 360 with a purple cam ported heads RPM intake thermoquad carb. It has a electric and mechanical fuel pump. I'm still running the 5/16 fuel line. When I floor it it pulls great till 3000 and won't rev much higher. Another time I was crusing about 2500 floored it and it pulled great to 5500 that's it. Now stock 5/16 from the sending unit to the electric fuel pump with fittings to the mechanical pump with fittings to the pressure regulator with fittings to fuel filter to the carb. Also have a fuel filter before the electric fuel pump and both are new. So it's a small fuel line and a lot of fittings Does this sound like a fuel restriction problem? Oh the carb was rebuilt by Rusty Rat Rod and he did a great job No bog and love the sound of those secondaries Thants. Jim