if the pressure is right, i would think more likely needs good cleaning. when my intake gaskets went i had all sorts of gunk in the valley, and all over under the valve covers. i cleaned what i could get too, then ran seafoam for a couple weeks in the oil then changed it. i always use valvoline oil, i think it keeps the engine cleaner. how many miles?

Idk pressure is just little under the 20 mark when idle and driving at 65 to 70 mph running 2100rpms it'* a little above the 20 mark usually or at te 20 mark, idk it seems to run fine and when I rev the motor up in park I can't hear no knocks or ticks so, I'm assuming the gauge is fubared along with the rest of the gauges, the fuel gauge acts funny and so does the volt gauge sometimes

maybe you have a poor ground in the cab. i dont know where it is on that. i would start looking above the drivers foot well area and disconnect it and clean it. the fuel gauge is a popular problem either the "butterfly needle" which is silicone leaked out of it. or the bushing on the sender that can allow the float to come away from the mount and the gauge will go from reading to not when the truck is moving.

I also noticed that at idle or while driving the dash lights like to flicker and when I have the dome light on u can also notice the flicker it'* weird