AN6 fuel line? rubber or rubber with stainless shielding over it or steel line from tank to pump with original style hose sections as installed at oem?

Reason I ask is I bought some China made high press fuel injection hose from a reputable parts house and started having issues like yours and found the the inner wall of the dual wall hose was collapsing and starving the engine.
440 with 750 EB and and high perf mechanical fuel pump.
Just a thought.

doc