What is the differences between Amsoils 5w30 oils? For instance, their series 3000 5w30 and their regular 5w30? I know that the series 3000 is for diesel, but what else? I am potentially considering switching from Amsoil's 0w30 to their 5w30, but wish to find their best 5w30. So far, people have been raving about their HDD Series 3000 5w30. What gives?