Power loss above 4000 rpm

[PHOENIX]

Got my truck on the road again.
When I get on it, above 4000 rpm, the power flattens out.
Not sure if the engine is not getting enough fuel, too much fuel or something else.
It happens right about at 4200-4300.
Is it normal for the fuel line going to the pump (mechanical) to move while the engine is running.
You can see if slightly shifting back and forth as the fuel is pumped through it.
If I hold the hose with my hand I can feel the fuel gulping through the hose.
The hose is new and is only like 8"-9" long (from steel line on frame to pump).