"If there are no dogs in Heaven, then when I die I want to go where they went." — Will Rogers
Dogs are better than most people, and alot of us know it.
Sorry for your loss my friend.
If current trans temps run 180f or less in summer heat, live with what you have. Bigger will serve no useful benefit.
There really is no min temp for trans temps. If you ran 120f in winter, you would be fine. I have never seen a "too big" trans cooler.
This is what I would do 👍. Changing grades from summer to winter may have helped decades ago, but, todays oils are so much better at cold/hot protection its not going to matter.