On the highway, the main two issues are aerodynamic drag and drivetrain efficiency. Newer engines have made great strides in improving efficiency, and the GX h

On the highway, the main two issues are aerodynamic drag and drivetrain efficiency. Newer engines have made great strides in improving efficiency, and the GX has a 6-speed transmission instead of a 4-speed, which counteract the larger drag of the boxier shape. The weight doesn't matter that much on the highway.