Truck simulator gear shifting

I am trying to create a truck simulator and currently I am stuck on how to implement the gear shift system.
With a car you would go from N -> 1 -> 2 -> 3 -> 4 etc.
But for trucks it’s quite different, it seems.


How would I implement something like this where a player can decide which gear to go to?
Lets say when I am driving in gear 3 and I want to switch to 7L or something.

Did you get any success in this regard. I am also gathering data and making some initial prototypes for a truck simulator game.