I have almost 20 K on my engine and have 5" TBE and EGR delted, I want to start using synthetic oil and was wondering if I need to run low ash oil since I have done away with all this nonsense now. I have considered royal purple and amosil as possible oils. Is anybody running these oils and what mileage would you start with the synthetic? I feel my motor still needs more break in time before I do this. With synthetic at what intervals would you change your oil?