The only thing consistant about cummins mpg, is that they are inconsistant to everyone elses trucks.

07 5.9 MegaCab 15city 15 highway no matter how a drive, babied or hot footed. 8-9mpg towing 8k tt 65-70mph, but i have to keep looking in my mirrors to make sure it is still behind me because the cummins doesnt even break a sweat when i tow it. Huge improvement over the 2 hemi's i had before, its like night and day.

 

Last I checked on the freeway was 21mpg with no load, and I got 9.5mpg avg towing 40' fifth wheel 1350 miles from Oregon to AZ which had alot of hills in between.

 

i have an 06 qc 4x4 with the 48re and 3.73 rear end and the banks big hoss kit. with it set to the economy tune and the cruise set to 75 most of the way, my trip from Twin Falls idaho to Atascadero california and back got me about 23mpg. in city i usualy see 16 to 18

 

never over 13-14 and that's driving conservitely