Modeling Collisions

I am making a edit of the wastelander where the size is increased and there is a ramp in the from of it but am running into the issue where collisions work for everything except for the fact where they collide with stuff where they shouldnt (shown in screenshot and yes i havent worked on any textures yet) Had first done it on the dump truck but it still ran into the issue. If you have a fix would be appreciated.