[bobbecky]

I'm surprised no one has brought up the reason for DEF. DEF allows the engines to run on a leaner mixture and still meet NOX emissions rules, and because they are running leaner, you get better fuel mileage. I also like the fact that I can stomp on the throttle and it doesn't look like a freight train with smoke belching out the exhaust. So the DPF is also a good item to have. All these things added into the system, and these rigs still have more stock horsepower and torque than previous generations of diesels.