I have a 2010 Aveo5 with an automatic and I was only getting 24 mpg, after about the 18,000-20,000 I began getting 31-33 mpg but the key is to never let the car rev above 2,000-2,500 rpm which going 55mph max, maybe 60 mph also it helps to let the drivetrain warm up so the car shifts into 4th gear. I also installed K&N air filter so I am not sure how much that helped. But it will get better


PS Until I had this Aveo I thought all of my cars would be GM (I had a Lumina before this and I loved it) but with my fuel economy troubles and with no help from GM my next car will be Asian