I have towed my Ranger 620, when fully loaded weighs just under 6000 lbs. and the back of my trucks filled with everything for 4 people with a Duramax and with a Ram Ecodiesel . With the Duramax I just set the cruise control and it very seldom shifted gears. The Ram eoc diesel I never used the cruise control except on flat stretches of highway. As would be expected the duramax had a lot more power and torque, but the Ram rode much better. The Ram also got 15.5 mpg compared to the duramaz 13.3. The wind plays a big factor on mpg. I bought the Ram because I wanted netter fuel economy when I wasnt towing. I have gotten as high as 29 mpg with it. I average about 25 on most longer trips. In the warmer months I averaged about 21 combined.