I have a 2018 Titan xd 4x4 diesel. I have been experimenting with different oils to see which got me the best efficiency. After trying several different options, the best by far is hotshot secrets green diamond 10w30 with a combination of their stiction eliminator. Currently getting 16.4 mpg city/21.2 mpg highway. Hauling a man lift the other day I averaged 15.5 mpg on the interstate. Amsoil is also very good, but this truck seems to be at its absolute best with this hotshot’s secret 10w30.