Mopar ATF+4 is not a group IV synthetic, it’s a group III fluid with a Lubrizol additive mixed in. For more information about Mopar ATF read this from Allpar:
Chrysler transmission fluids: 7176, ATF+3, ATF+4
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Group I base oils can have a mix of different hydrocarbon chains, with relatively little uniformity; these oils are the least refined. They are usually not used for autos.
Group II are the most common base oils in “dino juice,” with good performance in most areas except cold temperature viscosity.
Group III are called synthetic, and have high molecular uniformity and stability. Group III oil bases are used in most synthetic oils.
Group IV are chemically engineered stocks, arguably with the highest performance and longevity.