I am sure Dave will chime in here, but I would say along his thought processes and from I have learned myself using Amsoil for the last 5 years. I love Amsoil and like synthetics, HOWEVER, if you are not going to do longer OCI's, synthetics don't provide the amount of protection commensurate with the money you pay. You would do more than fine using something such as Valvoline Premium Blue Dino (Cummins factory fill)and running for 7.5-10k miles and spending less money. I ran my last diesel (Cummins) for 380,000 miles before trading it in and it was still running frickin' fantastic. I ran VPB 15w-40 at 7k mile OCI's and had NO problems engine wise. This is just something to think about. Synthetics provide the ability (sometimes) to run longer change intervals, not better protection over Dino HDEO, which are all very capable oils, IMO. And just on a personal note, I no longer use Amsoil. I switched to using Dino last month by realizing the the UOA's, inconvenience of having to order online, and not always getting comfortable results with UOA's, that I could just run a good dino, change every 10k, and be more than happy and well protected. Good luck on your search.