From what I've found, it's better to be harder on the gas to get up to speed and then try to be soft after that (ECO mode if you can get it). If I baby it I sit at 12-13 city, but if I'm more aggressive I'm 13-14 city. 3k miles, and I'm averaging 15 on the nose with pretty much 50/50 city and 55 mph highway. Haven't taken a trip since 500 miles in, but I was at 16-17 on the trip home at 1000 miles.
Hoping I get that slight bump around 5k that a lot of people say happens. I've put in a dry AEM drop in filter, removed carbon filter, use 91/93 etc. Nothing's changed it (didn't think it would). I did just install 2" spacers this weekend so I'm figuring I'll take a small hit from that, but I've noticed better highway mileage after having a bed cover on my old truck. Might offset the lift.