unfortunately 12.3mpg around down doesn't surprise me at all. that's typical for these trucks. the shifter stuff won't really help you. do u know what gears you have in the rear? that makes a little bit of a difference for driving around town.
if it bothers you, invest in a tuner like bully dog, it will firm up your shifts and probably boost ur mileage a few MPG
Thx for the welcome! Just had my truck a week and wondering why around town it's showing 12.3 MPG when im not driving it "heavy footed"? Recognized that the trans shifter has the ability to move up or down the gear and wondered if that makes any difference?