fuel pressure problems

[speedracerm1]

imca mod sbc 400 losing fuel pressure at the end of the straight.....pressure is at 10 psi out of the corner then looses pressure to about 5 psi at the end.... tried two different pumps,two different carbs, using a bg diaphram bypass one time then tried a holley pressure regulator.....
same result...anyone have an ides.....thanks in advance for any info....

[charcoal01]

Fuel filter?

[chapa9]

I would say since you've changed everything else look at fuel filter make sure you don't have fuel line collapsing, make sure fuel cell is vented.