I would like to propose adding two new scripting commands:

vehicle enableAutomaticTransition false;

Control weather the vehicle automatically changes gear (parameter true), or not (false). If turned off, will prevent the game from switching to another gear atuomatically.

vehcile setCurrentGear "gear";

This function will receive a string argument. The string must correspond to one of the gears defined in the "ComplexGearbox" class. It selects this gear as the current gear, irrespective of current drive parameters. If the automatic transition is disabled, no automatic change of gear will take place and switching to another gear needs to happen through setCurrentGear.

Rationale: Realistically modelling engines of some vehicles is next to impossible with the current setup. Even going from real-life values, the engine and gearbox will not behave like it should. This is particularly true for steep inclines. Sometimes, vehicles aren't able to climb because they use too high gears. In reality, you would, even on an automatic transition, switch from "D" to "1" or "2" settings. With the above mentioned commands, this could be achieved, as well as being able to achieve true manual shifting through appropriate mods.

Note, I'm not asking to make a fully functional "manual gear" setting for the game. I have no knowledge of the engine internes, but I would guess that these functions should be relatively easy to implement.