My Highway miles are actually down from 25. I own a Scanguage and that is how I know they work. Obviously, the A-rabs
and Big oil
are paying your rent. I got 25mpg highway for 75k miles. I am at 250 total miles. I am sure It will correct itself when I get a major tuneup. I have never replaced my O2 sensor. From Chicago to the Southern Side of Nashville with a quarter tank left (6times)