I've got an Aisin-Warner transmission in my Montero, which is capable of using both Dexron III and SP-III. I find the transmission shifts and runs much smoother with SP-III, so that is what I use. However, friend of mine has a similar truck of '98 vintage, with the same transmission. Since we're both due for our 25,000 mile service soon, we got all our supplies together and got a very decent amount knocked off. He works for a Chrysler dealer, and can get ATF +4 for significantly cheaper than SP-III and any Dexron III. Since we do cooler line flushes, and require at least 10 litres of fluid, that would be worthwhile. I've read here before that ATF +3 was essentially the same as SP-III with a different name, and somebody was mentioning that they use ATF +4 in SP-III applications. But seeing these transmissions are Aisin-Warner units that Mitsubishi has specified as capable of using both Dexron III and SP-III, I'm wondering how well ATF +4 would actually work (or not work!). On a side note, I notice Chrysler recommends ATF +4 in Mercedes 722.6 transmissions they've been using. Are those units modified in any way to use this fluid, or can I also safely use ATF +4 in a Mercedes ML500 with a 722.6 transmission? Input will be muchly appreciated, thanks!