I just can't seem to break my Amsoil SS 0W-40 habit. I feel that I need the 0W where I live but also need the 40. I don't tow very often, and when I do the weight is only around 1,000#'s or so. But 99% of the time I carry a very heavy camper, around 3,700#'s, probably quite a bit more. I often...