So I have had my 05 5.7 jgc for 3 months now and man the gas mileage is bad. According to the specs its supposed to get 14 city 21 why, but if I drive it like a v6 i will be lucky to get 11 mpg city. Normally I get around 10.5 with moderate throttle. If I step on it at almost every light I get 9 mpg. On a 60 mile hwy trip I average 17.5 mpg at a constant 65 mph. So is it running rich or is this normal? I mean I didnt buy this car for gas mileage, but this is srt bad without the power. I tried seafoaming it through the brake booster, gas tank, and the oil (didn't help) and I also changed the oil with mobil 1 synthetic 5w-20(also didn't help). I fill plus gas (89 octane) every time, which should also help gas mileage but it doesn't . No check engine light. What do you think?