Check that the tank is venting, a vacuum in a fuel tank, can cause all kinds of problems, correct fuel cap ?
As HD mechanic, (heavy earthmoving) fuel tank venting, has been the cause of several ongoing problems,
Fuel return check valve, or a failing fuel pump as said above.
Air in fuel supply, check all filters lines etc are sealing, piece of clear tube, just prior to the injection pump, gives good visual.
Sum cylinder heads, have a check valve in the fuel return, if common rail. If it's leaking can take the pump a bit of time to build enough pressure to overcome leakage and hold fuel pressure around the unit injectors.
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