Fuel Efficiency and the Yaris

[07liftback]

Went from 34mpg mostly highway to 28-30mpg mainly city driving. 34mpg was with 12 mile one way routes and 28-30mpg is with 5-6 mile one way routes. I had purchased some Denso spark plugs off ebay a couple years ago when I also changed my route, so I'm not sure if it's done anything to my mpg since I recently read that many spark plugs on ebay are actually counterfeit. I'll need to put my old ones back in and see if there's a difference in mpg.

However, driving like a granny from San Francisco to Los Angeles (400+ miles), I'm able to get 40+ mpg. Keep in mind that this includes drafting behind as many trucks as I can find and filling all my tires to above 40 psi with zero braking. Consistent 50-55mph on the freeway. If I drive normally from San Francisco to Los Angeles, I'd get about 30-35mpg (65-75mph). Not sure if there's something wrong with my car as it seems that my car is doing 20-40% worst than everyone else in this forum...