Hello Paul , im not sure what vac readings you should get at the egr pipe but it will vary with load as the duty cycle to the egr control solenoid changes.
Could it possibly be that the egr valve is getting opened under boost conditions thats where the code control pressure to small flags up .

Is the egr control solenoid the same as any other of the vac solenoids and you could swap it and see if you get different fault codes.

Can you drive on the road with your diag tool and watch boost pressure desired and actual to see if that gives you a clue what the boost is doing , you could watch duty cycle to the egr valve also .

HTL Lee