This wouldn't really be very hard to script at all. Sad that people made a meme of the topic.
All you would have to do is modify the vehicle's max speed, and run checks on the vehicle's current speed, changing things around as you 'shift' gears. You could make a believable automatic car, or give users the ability to shift gears themselves. Higher gears would result in worse acceleration, which might also be something you can change on a vehicle, so ramming it to fifth or sixth right away wouldn't work.
We can't have that, though, because it's not "blockland"y enough and it's "too realistic" as it doesn't strictly abide by how cars work previously, instead, it changes a major core feature of how cars work.
Don't believe the social stigma? See this topic.