This paper explores the performance improvements of a 2013 Ford Mustang Shelby GT500 resulting from changes to the rear axle housing. In previous work, described in [1, 2], the rear axle housing was optimized in order to minimize its weight. It was expected that the decrease in weight would lead to improved fuel economy; in this work, the vehicle was simulated for the EPA highway drive cycle (HWFET) both before and after the optimization of the housing, in order to quantify the changes in fuel economy. It was found that the optimization of the housing did produce a modest improvement in the chassis energy demand and in the fuel energy demand.