Has anyone used Amsoil synthetic Transmission lube 75W-90 GL-4 in their 1969 4 speed?

For the record, the Field Service manual for a '65 Dodge Dart/Coronet advises "Multi-Purpose Gear Oil SAE140" in warm climates and either "... SAE 80 or 90" or "Auto Trans Fluid Type "A" Suffix "A"" in cold climates.
You must realize that lubricants have changed dramatically in content in the
last 45 years or so, so I doubt these specs have much meaning now.
I've used Redline MTL synthetic lubricant for years with excellent results.

My $.02,

Jim