My bull has 151k miles on it and it's gas mileage has dropped alarmingly over the past 2 1/2 years. It used to get 450 miles to the tank... now I'm *lucky* if it makes 300 miles. My RPMS rarely see more then 3k and I avoid city driving. The route I take to work(most of my driving time) has only 5 stops over a 12 mile trip. So I guess my O2 sensors must be really fowled. Oh well another thing to add to the maintainance list.