0559 code, New pump head?

[68shifter]

2016 ISX15. About 600k. Someone demandated it previously. Just shut off going down the road and wouldn’t restart. Tons of emission related codes all inactive, 0559 the only active code. Lift pump works, had about 120psi at the filter head check port. Capped injectors etc, still no fire. On Insite commanded pressure of about 6k, only would see 150-200psi occasionally.

It’s had a new pump head at some point. But I pulled it apart. Both plungers are stuck. Once in a great while one might slowly fall down, but otherwise you have to pull on them manually to get them to move.

No shi#t anywhere I can see. Both followers look very nice. Lines, and cut open filter look good, I’m sure it’s a new filter though.

My question is-do I just buy a new head from KW or Cummins, or we have a local fuel injection place that remans them. I have them do a lot of turbos, 3406 and older cummins fuel pumps etc. I have not had too many isx pump issues. Just kind of in the fence which way to go. Thanks