I just switched over to amsoil synthetic to extend my drain intervals and protect my engine to the fullest. On the back of the container it says with the 6.4 L OEM drain intervals are needed. Does it only require this because of the DPF because some fuel makes its way into the oil during the regen? Im removing the DPF in about a month anyway. I was just curious because Im not really gaining the full advantage of synthetic oil.