This has been my experience; A/T gas mileage really tanks in stop and go city driving, even with turning the engine off at lights that are likely to last more than 15 seconds. On a level stretch of highway, I expect to see 38-40 mpg (with corrected mileage meter). Over 6 months of fill ups since having the software correction, the meter has been within about 0.3 mpg of the calculated mileage, sometimes above, sometimes below.