this is old but meaning to tell you guy i did the impossible and dont know how
i got a Bluetooth obd2 scan from ebay elm-something anyway
i went to west Virginia and i **** you not was getting 22mpg i did the math and elm said the same thing i did speed limit most times
99 silverado z71 5.3 street tires
no muffler on it stock everything
4 adults 2 kids in tow plus bags

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Man I got a 09 silverado extended cab v6 all stock but I have 24" rims I wish I could get 22mpg!!! I'm trying to sell these rims to get stock wheels and better my mpg