We have 02 yukon 5.3 4x4 with 125k miles. Around town, get 14-15, highway AND city driving. In city only, and running ac, yes, 12 is about it. I'm surprised about you getting 12 if you crank it, since mine drops to around to 10-11 if I'm rushing around alot in the middle of the duty day. Have stock tires, stock everything except K&N. K&N didn't help mileage, but does help perceived acceleration.