The (objectively) best Torqueflite-compatible trans fluid on the market until recently was Chrysler Mopar ATF+4. It is misunderstood by some to be "too slippery". In fact, ATF+4 is a significantly better fluid in every way than Dexron -II, -III, or -IV and ATF+ (+2, +3), and it does not cause, promote, or aggravate slippage. It maintains the specified viscosity across a temperature range that's wider at both the hot and cold ends, its lubrication and antiwear properties are better, it's more resistant to oxidation, sludging and varnish formation, and it smells better. It might even taste better, I don't know. There's an extremely detailed
Chrysler Engineering paper comparing every aspect (except taste) of ATF+4 vs. ATF+3, ATF+2, ATF+, and Dexron-III/IV.
Then along came GM's Dexron-VI, which is another extremely high performance fluid (where "performance" refers to all the things a trans fluid has to do...lubricate both metal-and-metal and metal-on-friction without screwing up the frictional elements' ability to grab and keep hold of the metal, remain stable when cold and when hot, resist foaming, resist oxidation, etc).
The RWD Torqueflites really don't
need anything more exotic than a good-quality ordinary Dexron (present spec is the newest Dexron VI, though you might still find some older or off-brand Dexron IIIe or other previous Dexrons on the market). I do run ATF+4 in mine, and they all seem happy with it. But the main point here is you really don't need to sweat it. You don't need to spend unnecessary money on exotic-brand fluids or special "race" fluid.
Some people advocate using Type F, an old Ford fluid. Fact is, Type-F is an archaic fluid with seriously inferior performance by just about every measure. Torqueflites will hold up fine with Type-F, which is mostly an illustration of how rugged the Torqueflite is. There are much funner ways of demonstrating that a Torqueflite is robustly enough engineered to withstand abuse than to use an (objectively) inferior fluid.
