Hi benebob,
It has been cool out lately
I have a transmission cooler and I measure the tranny outlet temperature going to the radiator before the cooler. I have noticed that the tranny takes a long time to get warm these days. This morning with an ambient of about 20F the tranny only got to about 145F by the time I got to work. That's even with driving at 60 to 80 mph for about an hour and a 1/2
I use TC lockup to judge the tranny temp. IF it locks up, then the fluid is warm enough. I also expect the tranny to lock up after about 20 minutes of driving. No problems this morning.
For those days when it is colder out I shut off the external cooler with a diverter valve. This bypases the external cooler.
The other thing to remember is that the fluid in tranny pan is colder than the fluid coming out of the tranny on the way to the cooler. The fluid coming out of the tranny has just gone thru the Torque Converter. This makes it hotter than the pan fluid.
I think it is a good idea to fully warm up the tranny before doing any hard driving in the winter.
I think your gas milage may be poor since you drive a short distance. Try letting your car idle for about 10 minutes before you drive off.
This may improve your gas mileage.