The suction side of the fuel system can cause this if a hose is pinched/kinked. The same exact trouble codes will set because the pump cannot get fuel PIP 4526 bulletin explains this from GM . Check all the rubber lines( cut off the outer foam cover to inspect) .
The most likely one to kink is the hose from the fuel injection control module to the fuel filter inlet on rt side of engine. Check all rubber lines, from tank to engine.
I have seen the pumps do this also, but not have the (hard to prime fuel filter ) concern.
If you can have someone hook up a bidirectional scan tool where they can control fuel pressure. Have them ramp up the pressure to 160 MPA ( 2250 psi )If it reaches this pressure then the pump is not your problem.
Injector replacement is a major job, and things sometimes don't get put back in the correct place. I would concentrate on the rubber lines on top of the engine.
I also assume since you are having a hard time priming the filter that you have already installed a new filter.
Verify there are NO air leaks at the filter housing to. This sounds more like a restriction than an air leak though.
If you need more info, PLEASE ask and i will help.