I've had mine since May '18. 4400 miles, mostly city. I get 11-12 in the city in normal driving. If I'm in Track/Sport/Custom modes... I can get as bad as 9.5mpg, since the trans holds gears longer and never shifts into 8th around town.
I've taken two 450 mile round trip highway jaunts, and seen 16+ averaging 80+mph. I live in Texas, so its very flat with little elevation change. It may get 17+ (I know some have reported this) if I slowed down to 70-75 as an average.
'18 Billet Silver Trackhawk
'02 Lingenfelter Twin Turbo Z06
'11 Corvette ZR1
'14 Audi SQ5