Is dexron and dexron III interchangeable?

Dexron III/Mercon automotive Transmission Fluid (ATF) is generally recommended as a replacement fluid for automatic transmissions meeting original equipment manufacturers (O.E.M.) performance requirements for current General Motors, Ford, other domestic and imported passenger cars, vans and light trucks where DEXRON II, DEXRON II-E, DEXRON III, AND Ford/MERCON fluids are specified.

Dexron VI is a partial synthetic which properties exceed dexron III by 100% in every area. Dexron VI can not be interchanged or repalced with DEXRON II, DEXRON II-E, DEXRON III, DEXRON-III/MERCON.