I go by what the manufacturers recommend. They spend a lot of time and money to determine what is best for their engines and transmissions. I don't know why this issue gets so convoluted and obfuscated when all one needs to do is read the manual. Ford, GM, Dodge, Caterpillar and Cummins do a great job explaining what is best for their engines and transmissions. I don't understand why so many get confused... If there is confusion about what they write in the manual, simply call the manufacturer and they will clarify it. At least that is what I have experienced.