ATF does not contain detergents. ATF doesn't have to deal with blowby the way motor oil does. ATF does contain dispersants to keep clutch particles in suspension.
http://www.lubrizol.com/DrivelineAdditives/AutomaticTransmissionFluidAdditives/default.html
The friction modifier characteristics of the fluid must be matched to the friction characteristics of the clutch material. The transmission rebuilder may select non-stock clutch materials that could work best with non-stock fluid.
It is easy to find real Dexron-III fluid. Look for its new name, Allison TES-389.
https://fdlrd.swri.org/Allison/ApprovedFluidsList.aspx?Id=2
http://www.lubrizol.com/DrivelineAdditives/AutomaticTransmissionFluidAdditives/default.html
The friction modifier characteristics of the fluid must be matched to the friction characteristics of the clutch material. The transmission rebuilder may select non-stock clutch materials that could work best with non-stock fluid.
It is easy to find real Dexron-III fluid. Look for its new name, Allison TES-389.
https://fdlrd.swri.org/Allison/ApprovedFluidsList.aspx?Id=2