From the handbook.

Click image to enlarge

Surely this is simply a consequence of the engine being unable to maintain the usual speed for a given throttle position. The effect of a steep hill is the same as towing a heavy load. Nothing to do with plugging into a trailer socket in my opinion.

There is a huge difference between the effects on the car of a loaded caravan and an empty light trailer. How does the car know the difference simply be connecting a socket? Doesnt make any sense to me.
If someone actually knows if the autobox is affected by attaching a trailer socket then please enlighten us.

If I attach my bike rack and plug in the lighting board - the car drives like normal as the extra load is only about 40kg, I imagine, so the autobox behaves normally. Jules

Those nice people at Jaguar Land Rover replied very quickly to my query about whether the auto boxes in the later cars might be remapped when a trailer is attached. Their reply was as follows:

The mapping does not change for the transmission, when a trailer is connected the load on the engine will be different and therefore the gearbox changes will be different. (it will hold onto gear longer before changing up)

exactly - cheers Simon Jules

From another Ford vehicle, a reminder about how important it is to torque up a tow bar's tensile bolts properly.



This resulted in a cracked chassis because almost certainly towbar bolts were not tightened sufficiently by the use of a torque wrench.

source:
 Jules