Anyone knows what causes the EPA Hwy ratings to be different on the sedans? When I purchased my 16, it showed a hwy rating of 42. But there were also several sedans that showed a rating of 40 on the hwy. When I asked the salesperson why the difference, he didn't know. Did they 17's go down 2 mpg? I noticed online that every 16 that are around here left have a highway rating of 42. Was Chevrolet "overinflating" the highway mpg?