I was in south Carolina with my 2014 6.2 with 3.73 rear and 20" wheels with stock tires.....tire pressure was 37 lbs. gas used was pump 87 octane.... was 40-50 farenheit outside air temp. I was pulling a tiny 4x8 utility trailer with a 1000lbs. or so of tools. truck also has a vinyl bed cover. truck has 1000 miles on it.
32 m.p.h. = exactly 28 mpg [go to 35 m.p.h. to get truck in 5th gear and then slow down to 32 m.p.h.on cruise control.....truck sometimes shifts to 4th]
40 m.p.h. = over 25 mpg 6th gear
50-55 m.p.h.= over 23 mpg 6th gear
towing a double axle 28' enclosed car hauler from Georgia ,, radial tires 80 lbs of air in 16" radial tires [under 6000lbs. estimated weight.and added cargo]
35-40m.p.h. = 17 mpg 6th gear
45 m.p.h. = 14mpg 5th gear
50 m.ph. = 12-13 mpg 5th gear
these numbers were accomplished with perfect tire pressure, ordinary pump gas, NO WIND CONDITIONS, 6.2 motor in a double cab 2wd., ltz with no extra options except block heater, cargo lights and tie downs, bed rug, tonneau cover, 350lb. driver. road must be perfectly flat. [rte 17, just south of Charlestown s.c.] I think this is chevy's lightest truck with the 6.2.....
the only difference between the 6.2 and the 5.3 is bore size and a little more compression