Man, I dont know what you guys are doing! I understand if you have offroad stuff like huge tires and skid plates, getting like 12 mpg, but I have an 01 V6 2WD and get 20mpg routinely combined city and highway (about 50/50). My worst tank since Ive owned it was 18 mpg, when I was flooring it often and going 80mph plus (I didnt have to pay for that tank 8) ) My best tank was 22.3mpg doing mostly highway and grandma driving.

My tips: a.) Dont go 80 mph on the interstates. (More air resistance and higher RPM equals worse gas mileage)
b.) Keep it under 2500 rpms while accelerating (if you have the same engine as me). Its slightly slower accel than average, but I deal with it just fine.
c.) I open the windows for air when on city roads...on 2 lane highways or anything between 50 and 60 mph or so I roll mine about halfway and the passenger cracked (less air resistance). For interstates or when its REALLY hot (90+), I turn the A/C the "2" notch of 4 for about 30 secs until Im cool (I point all of the vents at me when its only me in the car) then turn it off. Repeat as necessary (about every 2-4 mins for me)

Hope this helps