Stacey Jaeger

I have a 2014 GMC Sierra 1500 with 5.3 litre, with 400,000km. I drove it one morning and when starting later in the day it would crank but not start. I figured it had to be the fuel pump, SO i replaced the low pressure fuel pump in the tank. The problem persisted the exact same way, crank but no start. Checked a couple plugs and was getting spark. I then replaced the high pressure fuel pump under the intake. But the same problem persisted, it tried to start right after the high pressure pump replacement for a few seconds but then just cranks. I plugged in a better scan tool with live data and I can see the low pressure pump has the proper pressure but the high pressure pump is only getting 1-3mpa, when the scan tool says it should be 14mpa. The scan tool says the lower pressure fuel is in the 55-60psi range and it hold this pressure when not cranking. But the scan tool shows the high pressure fuel drop down from 2mpa to 0. I am not sure where to go from here, any recommendations or experiences with this condition? High pressure fuel rail sensor replacement?