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Anyway back on this topic, why the struggle with the fact that the base fluid really does effect functionality of a fluid? It's easy to know it does in temperature/viscosity behavior as well as oxidation resistance - so why not the frictional properties as well?
Let's get back to the focus of the total formulation.
The quality of the base oil provides the film strength characteristics, shear characteristics, varnish appearance, and oxidation. The better the base oil, the lower the varnish, lower oxidation, lower friction, higher film strength, and better shear resistance.
It is the additive package, and specifically the friction modification compounds (usually specialized complex amines) that determine the dynamic frictional characteristics of the fluid such as shift quality and anti-shudder for the frictional materials in the automatic transmission.
Now some of the other additives, such as oxidation inhibitors, help keep the oil more oxidation stable over the life of the oil; which is required for the more complex transmissions which tend to run hotter. Improved viscosity improvers in Group III oils also will help the oil maintain viscosity over the life of the oil as well. Pure synthetic ATF's will use little or no viscosity index improvers since their inherent viscosity characteristics are more stable.