You should follow the severe service schedule in SL. As for oil, 10w40 to 15w40. If you're in a hot hilly area you can go with 20 weight. FYI. Lower the number thinner the oil. If my memory serve me right, the first number is when the oil is at operating temperature and the second is when it's 'cold'
Factory will often recommend the thinnest oil they can get away with since they are trying to hit an emissions target.