I have 42k on my 6.7 the tailpipe is clean, except for a little rust. It is three months old. These trucks should never blow smoke.
Big Brothers, how weight are you pulling and what gearing. You don't have a sig. posted. I get about 13 to 13.5 pulling 12k. I have gotten as low as 9 but that was nearly 25k behind the ole girl. I have been impressed with the fuel mileage on mine.
__________________
07 CHASSIS CAB 6.7,AIR BAGS, G56
2007 3500 Quad 4x4, 5.9,AIR BAGS, G56, Edge with Attitude
95 F-350 5 SPEED 10K, FPR SHIM 4" Exh.