Fuel pump question

[Skman]

Took my 2013 ISX15 into shop to try figure out the fueling problem I've been seeing under load.
They hooked up the computer and did some testing...here's what they wrote on the invoice:
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Customer brought in because we're getting a low pressure fuel fault and loss of power at high load. Also seeing pyro temps climb when it happens.

Brought unit inside, checked fault codes, found many low fuel rail pressure faults.
Took unit for a road test, found the fuel rail pressure to drop 6000psi at full
load, brought back to shop, checked fuel filters, they are newer, so changed the
rail pressure relief valve. Took unit for a road test again, found the rail
pressure to still drop, checked for any suction side restrictions or leaks, no
problems there, checked the inline priming pump, it works normal, the high pressure
pump needs to come apart.
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So I'm still seeing the same problem after them installing a $500 relief valve for no reason....and 9 hours of shop time for troubleshooting.
They're thinking high pressure pump and lift pump should be changed. He suggested that the lift pump might be getting weak which after awhile caused the high pressure pump to have issues.
The fuel pump is the updated pump with steel plungers but the pump itself is probably original (800,000km/480 miles) so I guess it could be getting weak.
My question is:. I have another guy that I'd like to do it but he doesn't have the Cummins software. Do you need the software to change the fuel pump (for timing etc)?
Thanks