Just got back from 4 weeks on the road towing the 4500lb 5th wheel trailer (BW turnover ball/Andersen hitch). 5168 miles traveled and averaged 19.2 mpg. Trip went from central TX to NM, CO, UT, ID, MT, WY, NE and back thru OK. More than few switchback mountain roads. Parked and unhooked the trailer and drove the truck by itself which drove up the mileage, but several “all towing” tanks produced a high of 19 and a low of 17 mpg, albeit not driving over 70 mph while towing. One small glitch, while driving UP Monarch pass on Hwy 50, the “DEF warning, 500 miles to 65 mph“ warning came up on the speedo screen and couldn’t be dismissed with the steering wheel button. I knew there was plenty of DEF and after the climbing and on the downhill portion the warning went away and didn’t appear again. DEF usage was 7.5 gallons. Used tow haul some to help with downshifting on some of the more serious downhill portions, but not a big fan of the tranny screaming at 3500 rpm to slow the truck. All in all a great towing experience and the truck performed well!