The new process transmissions used ATF to help mileage, dealer mechanics put 30wt compressor oil (non detergent) in them at service. I used 50wt racing (non det) in some, worked good.
use multigrade, 70-140 or 70-90 so it is as thin as possible for milage, if you trans whines like mine does, a little lucas will keep the oil climbing the gears and dampen the noise. Lucas oil stabilizer rocks for old trucks.
