You can see my truck in my sig. I tow a 4K trailer 3 days a week, stopping at about 10 houses each of those days. I am not asking if Amsoil is better than Royal Purple or any other brand, I am just asking if Amsoil Synthetic 12 TBN 15W-40 sounds like what I should be using during warmer weather. This is what my local diesel shop guy has me filling up with currently. And yes, it is engine oil, not transmission or diff. Thanks!