Dextron III is what I run as recommended by my transmission builder. When I asked about running synthetic he said to save the money and change the fluid more often.

quote from the Valvoline web Q&A page
Quote:

What is the difference between DexronIII/Mercon and type "F" transmission fluid?
The Valvoline Type F transmission fluid is a high quality NON-friction modified fluid. Dexron III/Mercon includes friction modifiers in the fluid additive package.