Where is I good place for a reliable cp3Weak cp3, possible bad injectors, collapsing fuel lines, plugged fuel filter, sticking FPR is a few causes to that issue. Best bet is to fill out a signature about your truck what been done to it ect and use the search function. This has been discussed plenty lots of great answers on where to start.
Aside from running scan tool and shutting down each injector to see if they are working and also checked return fuel for 15 seconds of crank time and got 110ml return .. tuner gauges show a lot of info and more then I know about lol..Don't throw parts at it; take the time to properly diagnose it. You will not only save money but also learn more about the truck and how it works in the process. There are a number of things that can cause low rail pressure. What tests have you run so far to figure out the problem?