Thank you both for the prompt courteous replies. I figured the speeds driven had the most to do with the mpg and told her that they were prob going by the 55 mph limit, however my driving is mostly on interstate 69 out here in Indiana where the posted limit is 70mph. I'll take the mid 20's mpg rather than take the chance of getting run over by a semi. I have included the link for the Edmonds forum relating to the AVEO MPG and what their members had to say.
Chevrolet Aveo Real World MPG - Car Forums - Edmunds

look at replies #260 for the spark plug theory and reply #265 for the shift point theory