Ok I have about 10 things to say/ask in one post. First love the forum! 2nd I have a 2003 Silverado 2500HD with the 6liter gasser. I tow a 7000lb. enclosed trailer in city conditions about 90% of the time the truck is running. I asked an Amsoil rep about extended drain intervals and he said I could get 25,000 miles from their 5w-30 with Oil Analysis and a filter change halfway. I really just want to get 7500 out of an oil change. Is this possible without oil sampling? I don't have time to do the sampling and I rarely have time to change oil. I will do the oil changes myself. Are the oil filters that Amsoil sells necessary for a 7500 interval or can I go with a PureOne? Anyone have the part # I need for the Amsoil filter? Thanks in advance to all of you oil gurus!