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I don't think Dodge gives an official word on towing, just max numbers. These trucks are commonly over-loaded and worked hard all the time. This does not extend the life expectancy, but in the short term they are champs.
Generally OD is bad. OD is a gear described where the drive shaft will spin faster than the engine. This puts tremendous stress on the trans, and towing in OD will add even more stress. OD will create a lot more heat in the trans.
If you have a manual shift, I dont think your '14 is, then the 5th gear is an OD gear (and 4th is not really even a gear as it by-passes the trans gears and just passes the shaft rotation straight through where the engine and drive shaft turn in sync).
If you tow heavy it is tremendously important to have a trans temp gauge and drive according to the temp. Keep in mind that trans temp will lag a little behind what the actual stresses are on the trans as it takes time to heat up all that fluid.
180 degrees is getting hot, over 200 is really hot and I think 220 starts to burn the oil. When I run exclusively in 4th I can keep the trans temps way down, usually not more than 40 deg above outside temps. The engine will eventually heat up the trans some on multi-hour long drives.
As you get familiar with the temp gauge you will learn more.
The lower you can keep trans temps means the longer your trans will last.
Heat is coming from stress, and stress is bad on trans.
Use OD downhill (even 1 or 2% downhill) or with a tailwind, otherwise tow w OD off. You will want to keep speeds lower, maybe 65, to further save stress on trans. Air resistance, made more with trailer, is #1 friction factor to overcome and increases exponentially with speed increases.