John Deere Hygard hydro/transmission fluid?

Oils have different properties for different applications. JD recommends their brand because it has been developed and tested for their tractors which may run 12 hours a day [or more]. And they have to warrantee them. I consider them smarter than I am.

Chrysler tried variable rate trannies for a while. Special ATF was $20 plus a quart. The ATF for their regular trannies is ATF+4. The reason is that the lock up part of the converter engages smoother. Put the wrong oil in the wet clutch of a Harley and the clutch will slip forever.

There are experiments people can try, [within certain bounds].