Low fuel pressure at WOT

My car has been acting up and I’ve been having crazy fuel pressure issue. At idle pressure seems pretty normal 375-425 but while driving/cruising it will be around 1200-1400psi and then just drops down to 700-800 psi for a little and then goes back up randomly while driving. At wot im showing only 800psi at WOT. I’ve tried doing the prv test and it fails it show at 400psi then bleeds off from there and doesn’t build pressure. So I’ve tried replacing the prv and still same results I’ve also rebuild to hpfp with new o-rings I’m kinda at a lost here is it my spill valve or in the tank pump TIA !

 

Did you ever figure out this issue?

 

Any update?