This is the second CTD and we change every 25000km (17000mi) including the filter, oil is analyzed and comes out cleaner than most changing at 3-5000 miles using cheap petroleum oil. Compare dollar to dollar it is about even until the total milage/age of truck exceeds 200k then the synthetic will show cleaner inner galleries and less wear from cold stress starting and high heat deterioration from pulling loads. Amsoil is our choice because it is available to me as a dealer over the phone, Amsoil's business is synthetic oil engineering and our research amongst local users combined with their maintenance reports shows excellent histories of equipment usage and failures (lack there of). I dont necssarily agree with the marketing strategy as it can generate inexperienced people making money from published literature not real world hands on experience. There are a couple of other manufacturers out there but because we live North of the border and west of "civilization" they are hard to obtain. I have had access to company labs in the past while working for oil companies and the technicians have enlightening information about lots of oil and additive products when doing research. Driveline warranties tell a story as well about synthetics as torque stress rates have increased so does the need for superior lubricants which in some applications void warranty when synthetics are not used. PK