I replace egr sensor, dpfe and egr still code 0401 popping what it is

Because a DIY'er reads insufficient flow from EGR, that must be the issue, and now he has changed some very expensive parts and does not know why it didn't fix the issue. But that's what it said, LOL

How does one pressure test the fuel ?

With a fuel pressure tester, which includes a hose, fuel rail connector and fuel pressure gauge.