Compared to what I have owned in the past....it'* scary fast. You plant that right foot down, and it feels like a 200 mph gust filling the sails of a sloop. But in 4 cylinder mode, I pulled about 26 mpg on the highway this morning. Not bad at all.
I always liked the LS4...plenty of torque down low but still shines at highway speeds. I bet with a better intake and tune it could pull 30mpg highway.