well i finally did a drain and refill on my 06 tundra crew cab 2wd, i used amsoils new low viscosity atf for toyota ws. i drained a little more than 3 qts and put that exactly back in, it was very simple with help from my haynes manual. the reason im bothering even telling you this is because even just those 3qts, i noticed far smoother shifts, better than i ever remember with this truck. i will continue to use amsoil as i use it in every fluid in my truck my wifes mitsubishi and my honda atv. i know it sounds crazy i wasnt expecting it to shift so much better but i recommend it to anyone who is considering a transmission service soon, im going to do a drain and refill another 4 times at oil changes, it should be about 95% amsoil by then, im expecting good results each time, ill probably do a complete flush and drop the pan and filter replacement between 100k and150k miles......my point..... i recommend amsoil low viscosity atf........p.s. my truck has 48k miles for those curious and i do some average towing the four wheeler and such.