Did a little trip today very similar to your results. I filled up at half tank with 314.2miles on the car, 7.56gallons = 41.56MPG. DIC read 44.4mpg. My route was mostly highway with 1/3 with cruise set at 64mph interstate, 55-62mph two lane highways & tons of small towns. there was also a section of 30+ miles of 45-50mph roads. Range indicated if I kept driving at the same rate I could go 330+ more miles.Looks like I might hit 300 miles BEFORE the needle gets to the half tank mark this time...never seen that before. DIC currently estimating 44.3mpg....never had this high of an estimate this close to a half tank either. Maybe the re-gap is coming thru!
My car is also an automatic(1LT RS). Maybe this is coincidence but looking at the numbers on FUELLY.COM it seems the RS cruze ground effects have some aerodynamic benefits, most of the RS cars seem to get better MPG than the normal non-eco cruzes.