I ran Amsoil with 10k intervals from 40k miles up until I sold my Frontier a week or so ago with 128k miles. Sent the oil off for analysis every change to an independent lab (Blackstone) and the results always came back looking good. Never had a desire to go over 10k miles but was told in several of their reports I could go further. The key to extended drain intervals is a good filter as much as it is good oil.
