Well we just finished a short trip of about 1000 miles and the Acadia turned 9000 miles. We hit a lot of heavy traffic so the mileage was not great. The worst tank was 16 mpg, the next was 18 mpg, and the best was 22.3 mpg. The air conditioner was used most of the time with a lot of stop and go driving except on the last tank which was mostly highway driving. The ride and handling are impressive for a large vehicle and the comfort was good. We have had no mechanical problems as of yet, but the dash has now developed several rattles. I am continually disappointed with the performance of the transmission. I had the selector in L for most of the trip and manually shifted the transmission which worked fine, but that pretty much defeats the point of having an automatic. On one occassion I had the selector in D and was getting on the freeway when just as I needed the acceleration the most it upshifted into a higher gear and I had to floor it to get any power at all. I don't see the economy in having to drive like this. I think GM fooled the public and the EPA with this shift program. I'm sure it gave it better numbers with it up shifting so soon in the lab, but in real world driving I doubt it helps the mileage, and I think it is a major detraction from the vehicle's performance.