The most I've ever seen with keeping the DPF is 1 mpg over stock with a programming. The only way to add mileage is by using a DPF delete tuner and dpf delete exhaust as said above. The most common tuners we sell for delete kits is the Edge EVO Race or the PPE Hot+2 ET Race. Either of them seem to work very well, both are user friendly, and both will provide mileage gains on their respective tow tunes. We have tons of packages available, give me a shout at the shop tomorrow, and I can walk you through the options we have available.
Thanks,
Chad