Misfire on 8 Cylinders! '08 5.7

I bought this truck not too long ago, and after driving it for a while, I keep getting misfire codes for every cylinder (P0300-P0308) once my gas tank is around a half tank or lower. It's not a flex fuel truck, and I've replaced spark plugs and coil packs, but I keep getting a code even though the truck runs and drives very smooth. I get no hesitation on throttle, but I'm suspecting fueling- maybe a fuel pressure regulator? All help is greatly appreciated.

 

Hi,

I see that this is your fourth time posting this. I hope someone has some input but I haven’t seen this come up as a common problem. Have you tried replacing the intake manifold gaskets.?

 

definitely check for intake/vacuum leaks.