What are you looking to tow? How many people are in your family?
The 2008-2013/14 2500 Suburban/Yukon XL with the 6.0/3.73 with the 6 speed might get you 17mpg not towing on the highway. My Express with the 3.42 would get 18mpg all day long on the highway and over 20mpg at 60 mph.
I budget for 20mpg with the Suburban in my signature for highway driving. At 60mph I will easily get mid 20’s with our truck.
If you are looking at the 1500, I would highly recommend getting a 2015 or newer. My 2017 Suburban with the 3.08 tows as good or better than my 2012 Yukon XL with the 3.42. The bump in HP and Torque between 2014 and 2015 makes a difference. My 2012 also was not as consistent with fuel mileage and I would say it averaged 17mpg at best on the highway.
