desired fuel rail pressure vs actual fuel rail pressure

[Teamvi]

I have a stock cp3 and injectors on my 05 lly, if I really get on it my desired fuel pressure will be around 23k my actual will stay there for a little then drop down. I just installed a new fass 150 on it also? any ideas why I cant hold the fuel pressure? also have the ppe race plug

 

[chevyburnout1]

Weak injection pump or worn injectors that are returning too much fuel.

 

[Teamvi]

only does it at wide open, I can run a little lower on the throttle and it will hold it