The pour point is actuall a good indication of the "freezing" point, although it is not exactly the freezing point.

I doubt the hard shifting is caused by the ATF at that temp. LOL, I am in Big Rapids so it is colder than where you are. My (now sold) 87 300TDT (diesel) would start in any day. I miss that wagon.

It is probably caused by the delayed shifing (a feature) to warm up the engine as quickly as possible to reduce emission and increase fuel efficiency.