Newer fluids have more friction modifiers to make the fluid more "slippery". They do this to prevent harsh engagement, especially for the lockup convertor.
In an older transmission or anything race I never run anything but old school style fluids Dexron or type F that don't have as much of the friction modifiers.
Unless the builder or parts inside require a specific fluid then I go by those specs.
Exactly , my new to me 98 Cummins Ram must have +4 in it because the lockup shift is real lazy, I'll be refilling it with the dex/merc next time around ... I have a case of dex3 I bought probably 20 years ago , but I'm saving that for something special ...
