Thanks again for all the replies guys, the mileage I am getting is with Hard Top on,windows up, AC always on, I live in New Orleans, completely flat and at sea level, not sure if this has anything to do??
I took it for a 120 mile trip and got 18 mpg doing 70 mph, I did it when it had less than 500mi.
I have nowhere near to try the downhill test so I guess I can take it to the dealer and have them look at it.
Btw yeah I am looking at mpg not km/l.