I have a 4.6 2004 Explorer and 5.3 2005 Silverado. I drive around 15k per year on each and have been using Amsoil SSO in both with 1 year OCI's for the past several years. Even though I do think this is the best oil on the market, the price of other oils are so much less now I'm considering doing 6 month OCI with Syn-Power, PP, M1 etc. I only want to use synthetic and I started using Amsoil because it was the cheapest way to go with a 1 year OCI. Right now I figure it's the same price either way so it comes down to what is better for the engines. On a side note I've been thinking about switching the 4.6 to 0w/5w30 and using one oil for both engines. 5w-20 has worked fine but the Explorer has a on/off oil pressure gauge so I really don't know whats going on in there. Open to all facts and opinions!