I'm trying to determine which ATF to use this time in a 2000 Sienna. I used Dex III for several years until that was no longer readily available, then I tried using Mobil 1 ATF. While shift quality was improved over the Dex III (much smoother and softer shifting), I experienced some lazy shifts and what felt like occasional slipping with the M1. So about 20K miles ago, I replaced most of the M1 fill with with Dexron VI. Shift quality has been very good with the Dex VI, and while the feeling of slipping went away, I still occasionally experience somewhat of a lazy 1-2 shift when cold and when driving uphill, although not nearly as noticable as with the M1.
So with an ATF change on the horizon, my quandary is whether or not continue using the Dex VI or to simply try Dex/Merc this time since, according to my understanding, that is more or less the continuation of the Dex III spec. What would you all recommend for an Aisin-Warner unit like what is installed in this Sienna? Transmission still seems very healthy overall after 108K miles, and I'd like to make it last as long as possible.
So with an ATF change on the horizon, my quandary is whether or not continue using the Dex VI or to simply try Dex/Merc this time since, according to my understanding, that is more or less the continuation of the Dex III spec. What would you all recommend for an Aisin-Warner unit like what is installed in this Sienna? Transmission still seems very healthy overall after 108K miles, and I'd like to make it last as long as possible.
