If you are a runner you should not increase mileage by more than 10 % per week. (sportsinjuryclinic.net)
This problem clearly illustrates the situation: the overdrive button just allows the transmission to select an even higher gear, primarily for increased mileage at high speeds. (mechanics.stackexchange.com)
The «inflation» argument to justify increased mileage requirements is rather silly. (travelskills.com)