I have used Amsoil Syn ATF for almost 30K miles in my 03 5spd box, which included some pretty good wheeling, hard racing on the dunes, long and hard mountain roads with a fully loaded truck. No ill effect adn actually shifted better than the ATF Type-IV.
Teh big ballbreaker is the 03+ trannies which takes Toyota WS fluid (which is full synthetic), no replacement available for that AFAIK. Just get the Toyota fluid. It willprobably be a good idea to swap it at 60K if you work the tranny hard anyway, maybe I'm old school but there is no such thing as a life time fluid (unless you want to reduce the lifetime of the component ).
Your owners manual should state what to use.
Teh big ballbreaker is the 03+ trannies which takes Toyota WS fluid (which is full synthetic), no replacement available for that AFAIK. Just get the Toyota fluid. It willprobably be a good idea to swap it at 60K if you work the tranny hard anyway, maybe I'm old school but there is no such thing as a life time fluid (unless you want to reduce the lifetime of the component ).
Your owners manual should state what to use.