Dave,
I really have no idea about the gas mileage, I am waiting to try to drive it normally for a little while before I check it-can't seem to keep my right foot out of it. It does seem to get much better than the six though. I can't believe how much better the car is as an around town car. Better torque, steers easier, smoother running, just start and drive. No cooling issues so far either. Good luck and feel free to PM me if you have any questions I can help with.
Mike