In my 08 CC/LB 3500hd SRW unloaded i get 15-16 mpg around town to work etc. on a good long trip 18-19 mpg, Its completely stock with dpf and all (gasp!) Pulling the old mans 9500 lb bumper pull trailer i was down to 13-14 mpg, by no means a flat or straight road, way better than his 5-6 mpg...