Are your numbers calculated by the Blazer's computer? I ask because I've kept a manual log for my 2010 Equinox and its computer consistently averages two to three mpg better than my manual entries. Pisses me off.V6 less than 500 miles on it. Drive it like I stole it 80% of the time. Mix of dirt roads and highways. 17-18 mpg. On two 150 mile highway trips averaging 80 mph I got 21 both times.