After all the reading about fuel dilution, due to regen cycles, I don't think your mileage will increase. But I am right there with you. Just bought a 2011 3500, SRW 6. 7 and am getting about the same. Had my truck 2 weeks from the dealer and it has been in the shop for the other 2 weeks, waiting on an "Exhaust pressure sensor". Not sure what to think. But do know, I wish I had my 06 3500 SRW with 5. 9 back. Lost it to a moose in the road and about 30 yards of trees and 1 utility pole. Good luck with yours and will be looking to see if you do get an increase with mileage, along with mine.