The US EPA has revised their method of determining the MPG of vehicles. The revisions apply to vehicles as far back as 1985. Check the revised MPG rating for your vehicle on this site.
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My 1997 Nissan 4x4 pickup went from 17 city, 19 highway, and 18 combined, to 15 city, 18 highway, and 16 combined. I still get a percentage better than the old EPA combined rating.