Towing with our 2500 HD we have gotten at best 9.5, worst was when we brought the camper home bucking a head wind with gusts up to 30 mph, we got 6.5. But, I too drive it like a grandpa. Not towing the best I have gotten is 17.5. I'm satisfied with the truck completely.
2015 Chevy 2500HD Z71 Crew Cab 6.0L-V8, 4:10 gears
2015 White Hawk 28dsbh
2013 Jayco Jay Feather 23b (traded in)
2009 Chevy Silverado 1500 5.3L HD Tow Package (traded in)
Equalizer E-4 WD Hitch