I bought a new 2002 Dodge Ram 1500 4dr truck with the 4.7l engine.So far I have 10K on the engine,and have changed it every 3k with filter.I've been using the Mobil 10w30 and either Fram or Purolater filters.Is this a good oil for this truck,or should I go with a 15w40?? This truck is mainly used for going to work,but I do tow a race car/trailer combo that weighs in at 5K,and I live in Florida.Thoughts/suggestions??