I have had good experience with Mobil 1 in our family's Ranger, but that's a MANUAL tranny. Go figure- a manual that calls for ATX.
But it shifted way better.
I would NOT do any additives.
Also, why does yours take time to go into overdrive? Fluid temperature should not influence shift points. Ambient temp might, but even then I would be surprised. In fact, I know it doesn't on mine...
Randy
