Sometimes when driving my van seams like it will hardly make it going up a hill, it starts shaking and kind of like its putting out, sometimes it does it just regular driving too, and this light comes on and sometimes stays on, or just flashes too, the light is right to the side at the top of my pedometer, so have to go a a five hr trip in about a month, and I don't want my van to break down on me, it does have a lot of miles on it.around 120000, does anyone know what it might be? so I will kind of know how much it might cost, before I take it to a mechanic?