Ok I know I haven't been around for a while! Anyways, recently bought 12 Ram 2500 6.7 HO 4x4, mileage 281,000! I know the truck personally and good friends with the guy I bought it from. Was driving down the road the other day about 65mph and it started acting like it didn't wanna go, Pulled in grabbed a bite to eat, get back in and it was little hard starting, and kinda sluggish in o/d. Get back to the shop and decided to replace the fuel filter, now it wasn't dirty and kinda slow to fill back up, so replaced intank lift pump have good fuel pressure and flow to filter. Truck will try to hit once and that's it, accidently cleared the codes but do remember that it said something about low fuel rail pressure. Hooked up diagnostic tool again and monitored fuel pressure it's running about 4,000 at starting but will not start, no tuner, bone stock. Any ideas where I need to look? I'm outta ideas!!!

You said you took the fuel supply line off the pump?  There are 3 lines to the cp3.   A banjo bolt, a quick disconnect and a steel line that you need a wrench for.   Which line is it your referring to?

 

You said the banjo bolt had minimal flow??   That is the pump return and minimal flow might be normal.