Give an automatic a fresh fill of fluid and a new filter at least every two years if it has a filter you can replace, annually if there's a strainer that's not normally serviced.

On all but a handful of cars, you've got to drop the oil pan to drain the old fluid and gain access to the filter. Many filters seal to the oil pump inlet by an O-ring, so whether the O-ring is on the filter or a neck that projects from the pump, be sure to replace it and seat it accurately. Otherwise, the pump may not pick up enough oil, affecting transmission performance. (Usually the filter, pan gasket and any O-rings are packaged together.) If there's a magnet in the drain pan, clean it before reinstalling.

Also, there are aftermarket in-line filters, similar to an oil filter, that you can splice into the cooler lines. Heavy-duty use, like towing, would make an auxiliary cooler a good idea, as well. Put the cooler into the line ahead of the stock cooler in the radiator the idea is to make sure the Automatic Transmission Fluid (ATF) isn't overcooled. The radiator will actually warm the ATF to the proper temp even in the depths of winter.