Not to specifically resurrect this thread, but . . .
Until Chrysler started recommending Dexron (the original) in 1967 or 1968, the prior spec was the "old" Type A, Suffix A atf that everybody used. Ford Type "F" and Dexron appeared in the same model year.

CAR LIFE magazine had an excellent article on the fluids' differences and similarities, all in the quest of "the smoothest shift". The article claimed that in the then-new THM400, GM put more capacity in the clutches so they could make them slip upon initial engagement, which is what Dexron did. Upon initial engagement until clutch "lockup", the rate of slippage was greater, then decreased to "no slip".

Ford went another way. They used less clutch capacity to temporarily over-load the clutch to cause initial slippage until clutch lockup. Their Type "F" fluid had a grabbier initial friction coefficient that made up for the intended slippage in the clutch pack. Therefore, with that initial grabbiness of the fluid characteristics, Type "F" became the defacto "higher performance" fluid at a time when only B&M TrickShift existed as the performance atf alternative. From initial apply to full lockup was of the same time period for both approaches.

In TorqueFlite 727s for 1966, Chrysler went toward the cherished "imperceptible" shift by replacing the "flat" steels (1965 and prior) in the clutch packs with "wavy" steels. That in itself, replacing the wavys with flats, makes for a quicker and firmer shift with normal atf, but unless you know what's what, many might never know it. This was with the old Type A Suffix A fluid.

In the Chrysler "Police Car" book, it mentions that in 1962, the CHP's new maintenance director desired to cut costs, so he bought 20W motor oil and used it in the TorqueFlites as well as in the engines. Only rule was that after an extended pursuit, the unit come in for an oil change of the trans. It was also noted that other brands of transmissions did not take kindly to the 20W motor oil in the automatic transmission.

So, by 1969, Ford was all Type "F" (the incognito "performance" atf), with Dexron in GM and Chrysler automatics. Dexron II addressed atf cooler corrosion issues (trans cooler in the radiator tank), as earlier mentioned Dex II-E was for electronic conrols, and Dex III soon replaced it in the 1980s decade. Dex II-E had a quicker shift than Dex II, by observation, but adding the GM Automatic Trans Conditioner additive (usually for higher mileage units) to Dex II resulted in a similarly faster shift. Dex III came in about the time of more sophisticated lock-up torque converters.

The newer Dex VI is a semi-syn fluid that GM claims is fully backward compatible to all GM transmissions to model year 1949. An Allpar.com article has some great information on the longer service life of the semi-syn OEM atfs. Plus that Chrysler desired backward compatibility, but full-syn had some issues with seals, so semi-syn was used.

In our then-new 1966 Chrysler, upon cold starts, the trans would have a little delay in things getting up to pressure. After the first transmission service, it became necessary to start it in "N", rather than "P", to not have any delays. Allegedly, the factory-fill fluid was a multi-vis fluid, but the replacement was not.

When the LH cars came out, the first atf spec was Dex III + a Chrysler additive. Using just Dex III would result in decreased clutch friction life. The trans controller would monitor for slippage and increase line pressure 100 times/second to combat it. With the friction characteristics of Dex IIi alone, it would hammer the friction material from the facings in the converter and clutch packs. That'w what I read and also confirmed that the fwd UltraDrives were notorious for "running fine" and then wouldn't move after they were parked. The module adjusted line pressure to combat slippage right until it was metal-to-metal in the clutches.

The Chrysler ATF+__ fluids came into being with the UltraDrive and later LH cars. As I recall ATF+3 was backward compatible for earlier automatics.

In later years, many changes to frictional characteristics of atf were made related to converter clutch issues. Some OEMs now modulate "lockup" levels (between 0 and 100%) depending upon operational environments.

GM is not licensing Dex III any more, as Ford is not licensing Type "F" any more, with "Dex/Merc" being the default replacement for Dex III.

Earlier on, it was claimed that if you used Dex in a Ford Type "F" spec transmission, the clutches would cook. Or if you used Type "F" in a GM trans, it would break, but only putting Dex in a Ford Type "F" trans might cause problems. Note that after a particular model year, Ford spec'd Dex for a few years before their "Mercon" fluid family came out. It's suspected that Mercon IV is very similar to Dex III but customized for Ford's desired converter lockup characteristics . . . plus some shops use Mercon IV where Dex III is spec'd

Many trans shops have their own likes and dislikes for trans fluid specs and what they will or will not work in. We've gone from a generic Type A Suffix A fluid spec to very specialized fluid specs over the past 50 years.

Back to the TorqueFlite without lock-up torque converters, historically you can use pretty much any common atf available. Some are a little ligter viscosity than others (faster shifts and better fluid flow), but common Dex III seemed to work just fine. In racing applications, a syn fluid (as Amsoil) works good, too.

The newer fluids have more additives and friction modifiers in them than any prior atf, with some being semi-syn or full syn. As GM claims Dex VI to be backward compatible to 1949, is a semi-syn, that migt be a good choice of "normal" atfs. There are plenty of higher-performance atfs, too. In any event, watch for color and smell changes in whatever atf you use and change it if those things change significantly.

CBODY67