The confusion is caused by Toyota changing transfluids every couple of years.
1998-2000? - Dexron III - Lots of Aftermarket options
2000?-2003 - Toyota Type-IV - Valvoline Maxlife, Mobil ATF 3309 and Amsoil (Synthetic)
2003- - WS (World Standard) - Don't worry it's a "Lifetime" Fluid
The main goal of this thread was to find out what options were available for Type-IV tranny fluids as it was pricey. The end result is that Amsoil technical support said that their ATF met Toyota - IV standards without reformulation (indicating not much difference form regular Dexron III) and since it is Dexron III compatible also it can run in any of the 4-speed auto trannies. The new World Standard (WS) is a totally different animal that apparently never needs changed or even checked
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My truck has always seen a Dexron III compatible product since it is a 1998.