EPA changed the test procedure in 2008. The new version of the test is run with the air conditioner on and with harder acceleration and a few other changes. The old test was completely unrealistic (hw test was run at 45mph with granny like acceleration), the new one is slightly unrealistic. If you go to the epa fuel economy website they give adjusted ratings for older cars that are 10-20% lower than what was published on the old test. There was also a change to how horsepower numbers are calculated and published a few years earlier (05 or 06). The old system underrated accessory loads.