A few things...

Your best bet is to look for a user forum for the specific vehicle that you drive. Lots of these are out there, some better than others, but the knowledge base is excellent, and typically includes machanics, etc.

I tow with OD, both with the RV and the Explorers. The only time I change to D is on inclines. You know you have a problem when the tranny keeps shifting from OD to D and back.

I don't think tranny coolers are over-rated at all. Get the biggest one that will fit your vehicle. Heat is a major enemy of auto trannys.

As mentioned, drain plugs are helpful. You can get an aftermarket kit (involves drilling a hole in your pan, may not be for the squeamish).

Hope this helps.

Mike