I know it's been discussed on here more than once but I need to know! My brother has a 2005 Dodge 2500 4x4 with a Cummins and a 6-speed manual trans. He lives in Las Vegas where as you know it gets very hot. He bought the truck new and used Rotella oil the first 5K miles and then swithed to Amsoil. He contacted and told Amsoil what he used the truck for which is moderate towing and around town use. Now I know that they didn't develop a special blend of synthetic diesel oil just for him but they did need to to know everything about his truck. They sent him the required amount of oil and their oil filter and told him to run it for 25K miles before he changed it. At 22K miles he noticed that the engine was 1 quart low on oil so he changed it and the filter. He then put 25K miles on this oil before he changed it and the filter. The oil was just as clean at 25K miles as it was when he poured it in. Amsoil also has a 100% guarantee that they will replace your engine for free if it fails because of their oil anf filter. Big diesel semi's are running 100K miles between their oil changes with the same guarantee. My brother also said that his truck ran quieter and had more power almost instantly when he used Amsoil the first time. My brother is not one to say these things if it wasn't true. Has anyone on here put that many miles on Amsoil diesel oil between changes? Sorry to be so long winded but inquiring minds gotta know!