(1) “Gross combination weight rating” or “GCWR” means a value specified by the manufacturer of the power unit if that value is displayed on the federal motor vehicle safety standard (FMVSS) certification label required by the National Highway Traffic Safety Administration.

  (2) “Gross vehicle weight rating” or “GVWR” means the sum of the gross vehicle weight ratings, or the sum of the gross vehicle weights of the power unit and the towed unit or units, or any combination of the gross vehicle weight ratings and the gross vehicle weights of power unit and towed unit or units that produces the highest value. The gross combination weight rating of the power unit shall not be used in determining whether the vehicle is a commercial motor vehicle when that power unit is not towing another unit.