ISX 12 code 4726 and 0559

[FarmLife]

I replaced the high pressure fuel pump. Mostly have the same results. Still has low rail pressure. I ran the injector leak off test and it set 2 new codes. Codes 3741 and 3727 and still has the 0559. I ran the cylinder cut off test and when I cut off #6 the rail pressure becomes almost even with actual vs commanded. I then capped off the the common rail going to #6 injector and actual vs commanded is almost even. When I take the cap off #6 and try to start the engine it will not restart and has low rail cranking pressure. Put cap back on #6 and it will restart.

Am I wrong in thinking I need to replace injector #6. I have cut off and capped all other cylinders with little to no change in actual rail pressure. I have 3 sister trucks and I am thinking to swap one injector at a time and see what happens.