If you go back and look at the 5.7 auto vs. manual... I think you will see that the difference is minimal. I guess due to the gear ratio in 6-speed and the fact that it keeps the RPM low at operating speeds. I can't say for 100% certainty that I have my facts straight. I have read so much over the week that I can't place all the facts as facts. But if I remember where I saw the gas mileage specs I'll be sure to post.