My new 2020 2500HD Duramax only has 193 miles on it. 95% or more has been stop and go city driving and the computer is reading 9.8 mpg. I am sure it’s my driving as I am enjoying the torque! I will be taking it easy to see if I can get the 12 to 14 mpg city (Real world, calculated) I was getting on my 2016 Duramax.