Fuel Pressure Issues. Multiple codes

[Matrice87]

Hello, 

Recently my gfs 2018 Sierra 5.3 L  (110,000kms) has been having fuel pressure codes come up causing her truck to go into reduced power mode.  I changed out the fuel pressure sensor on the line under the box with no change.  From research it’s fairly common for the high pressure pump to go that is up front under the intake, is that possibly the culprit?  As far as the fuel pressure regulator my understanding is that they are in the tank on the pump in these newer trucks? Way of testing there the regulator?  Codes are as listed P00C8, P00C6, P0089 and P228C. Going to try and fix it this weekend.  Thank you so much for any info. 

[silveradosid]

start by reading this https://f01.justanswer.com/Bluegorilla/2a46e6b8-ea48-45a0-81b6-46c595be5107_My_Boot_Camp_printed_document-3.pdf

[Matrice87]

Thanks for the link.  I’ll see what I can do with it this weekend.