Cat SDP help

[HamblinTrucking]

Alright who's the cat pros in here? I have a 2011 t660 with an sdp in it. It had low fuel pressure when I bought it. I changed all the check valves and the transfer pump. Im at 79 psi at idle now(id prefer it be 85)(thats the middle of the spec i believe). The real issue is the boost though. It won't build more than 35 psi usually and its really lazy making it. Then on very rare occasions you can feel what seems to be "full power" and it will build 50psi and pulls hard. Its a factory 625hp truck demandated. Iva still functional. Do I need to block off this cgi pipe people are talking about? This is my first cat. Maybe its in a limp mode of sorts?