A method is provided for modifying a cab assembly of a Class 5 or higher truck. The cab assembly includes a cab. The cab has an original cab height from a cab bottom end to a cab top end thereof. The cab includes a bottom region, a window region located above the bottom region, a roof region located above the window region, and a window defined in the window region. The method includes: cutting the cab through the window region to divide the cab into a top section and a bottom section; and thereafter joining the top section or a replacement top section to the bottom section to form a modified cab, wherein the modified cab has a modified height from the cab bottom end to the cab top end that is less than the original cab height.