This is what my repair manual says:
PROTIP: The factory recommends Type F transmission fluid for standard factory performance. Based on individual preferences, if the owner is wanting a quicker shift out of first gear, then Dextron/Mercon III is suggested. If the owner is wanting the engine to stay in first gear longer, then SAE30 motor oil is suggested. SAE 30 is not recommended for colder climates! All of these oils can be purchased at any auto parts store.