Hillclimb is recently added competition in the racing world, and it includes very powerful vehicles, trucks mostly, which are meant to go up hill to the furthest point of the track. The catch here is that these races are held in the desert.
The tires don’t have much grip on the sand track, and they are going up hill, so the engine needs to be powerful and the transmission needs to be modified as well.
With a normal transmission and differential you cannot go one meter uphill on the sand. The vehicles are monsters with enormous engines.