As you've seen, the EVIC is an overall average... I've got close to 4K and I'm getting 13 or so around town... my limited highway driving has been 16+
My overall average per Fuelly has gone down a little because of the 30ft Airstream I was towing... even then I was getting just over 10mpg.
Sitting at a light you are going to suck gas... go easy on the throttle and keep it at 70 (or less) on the highway... the 8 speed is light years ahead of the old 6 speed, also realize it is geared for towing and wants to rev high to hit the power band. These are HD trucks, they don't get an EPA MPG rating because it generally suck, however, I will say my 2500 is getting the same, if not better, mileage than my 2019 1500.