You need a better mechanic. The EGR system is simple to diagnose for anyone
with a handheld vacuum pump, a scanner, basic understanding how things work
and a manual.
Now that you replaced the valve and the DPFE (presumably it's not connected
backwards), we can assume that there is indeed insufficient flow and it is
not caused by a malfunctioning valve. Still quite a few options: bad
regulator (solenoid), no or low vacuum supply to the regulator, an
obstruction between the regulator and the valve, clogged EGR tube (at the
restriction point perhaps)... What should I say? You can keep throwing parts
at it, or try to diagnose it. Your choice
A very simple test to see that there is no major obstruction anywhere in the
EGR path is to let the engine idle and force the valve open with a vacuum
pump (or perhaps by smartly sneaking a tee into a vacuum line somewhere).
When the valve opens the engine should stall, or at least hesitate severely.