Fuel filter gauge shows restriction sometimes

[Bigstank]

hey got a question for the fuel system on this demandated CM871. My fuel filter gauge will show 5-ingh and the truck runs crappy as in low power & bad fuel mileage and it also has a throttle vibration but if i shut it off and let it sit for like 30mins and restart it. It runs excellent with the fuel filter gauge showing only 1-inhg. Where should I start to find what is causing the fuel flow restriction? The engine was inframed back in sept 2019 by haggai so we all know it was done right. Thanks guys