since i have access to a lift, i do 3x3x3 every 20K or so. Since getting my first tranny replaced, my fluid doesn't really look bad at all and doing the 3x3x3 method seems to be the best way in my opinion. I like the spoiled milk example someone made earlier. Good way to look at it. I keep my receipts for my tranny fluid purchases, but that would be one dirty ass dealership to require receipts for their fluid service when the trannies are known to have drama. That is some BS right there if you ask me.