A855 - 5 Speed

I just don´t get the need for the 5K overdrive . I just got back from a 2 hour interstate drive . Barracuda , mild 340 pulls hard , 833-4-speed , 3.23 sure-grip , ran 75-85mph the whole way 16mpg at the fill up $2.39 a gallon .car drives awesome ,I love it ,I paid less then your transmission for the whole car 20 years ago.