Our 2009 Silverado 4x4 with 5.3 liter V8 towing our 17 ft Egg Camper
gets anywhere from 13 to 17 mpg depending on speed, wind, hills, traffic, etc. Ours will cut back to 4 cylinders depending on conditions even towing. Non-towing mpg varies from 18 to about 21, though 21 is rare. The ONLY time I'd drive over 60 while towing would be passing somebody.