[Big Dave]

Anybody here think the Tier II diesels are not more efficient if you lose the DPF?

All filters induce a pressure loss. That is back pressure. A diesel is very sensitive to back pressure. Back pressure is what works (non-Jacobs) diesel exhaust brakes.

The DPF is an example of making a lot of people pay a very steep price for an infinitesimal benefit that acrues to a very small part of the population.

And the DPF defeats the strength of the diesel. If I had one, the DPF would be on the garage floor as fast as I could cut it off.