Hi Mark,
What was the pressure reading before DPF after you fitted new unit.
I did not think that 3 psi was a high reading at all with the non genuine unit fitted.
I have seen 40 to 50 Kpa (6 - 7 psi) on Zafira's before re-gen without bringing on the service light.
After Re-gen these run around 3 - 6 Kpa on a light to medium throttle.
The Zafira system seems to reach 80 Kpa (11-12 psi) before service light comes on relating to the differential pressure.

Cheers, Tony.