I have just over 5k mi on my RS. On my daily 9.5mi round trip commute to work via city streets, I get about 16mpg. This is about 1-2 mpg better than the 2015 Acadia I was using (with the V-6). It's only if i add in a bunch of freeway driving can I get even close to the rated (EPA estimated) 19mpg city. I'm not sure what the EPA considers city driving but I've never come close and I drive it with fuel economy in mind (very easy to and from stop lights and signs). Freeway mileage I get in the mid 20's @ around 75-80mph which isn't too bad for punching a large hole in the air (drafting helps). In general, I don't like they way the GM engineers mapped the engine and trans. I think they could've dropped the shift points and added a bit more boost down low. The engine feels to me like it hangs at 2500-3k rpm waiting to shift under light throttle and relatively low load. I think the low end grunt is there to let it short shift and pull under light throttle but it just doesn't. I'm sure this was done to benefit emissions or mpg but mpg isn't that great anyway. Under freeway cruise, the power is good.
