What is my problem?

[silver6.0]

I'm experiencing an annoying problem with my fuel pressure. My fuel system is as follows:stock lines with 6.4 banjos, an airdog II 165/75(turned all the way up) feeding the stock regulator(set around 60psi with the BB mod)and I removed the engine mounted filter and stand pipe. I'm running the sct canned 120hp tune. My fuel pressure sits around around 60psi at ide and cruise and pretty much all driving conditions EXCEPT at wot. When I lay into it the pressure drops around 50psi or a little less. I've got stock injectors and pretty mild tuning so i wouldn't think my fuel pressure would move at all with the airdog...

Should I consider this normal? Is the stock regulator spring suspect? I'm kinda lost here

Thanks

[06 KR]

I have the same setup as you minus the banjo's and the stand pipe removed. I sit at 60 psi and at WOT i hit 55-56 on a long run. I am running the SCT canned street tune. But with my airdog is still at the factory setting. I wonder if its the tune? I also wonder if the sending unit to your gauge might be a little off?? other then that I also am at a loss.

[silver6.0]

Just trying to get a second opinion before i start throwing parts at it