For the purpose of towing, Auto or Man?

[Windsor342ci]

Hi guys,

Over the weekend I done a bit of towing. 1200 kms to be exact. Lets round it off and say I was towing my max braked tow capacity.
The car I was using was my 4wd. 2.7L TD Pathfinder Auto.

Now on the way to work this morning I noticed it only happen once, but as it went To go into the next gear, it revved a little more then slipped into the gear. At this stage my assumption is that my bands are slipping. Not this is not a concern for me as I will happily fix it. Admittedly the work horse is a little older now with just over 330,000kms on the clock. I had the box serviced less then a year ago. So understanding it ageing, but here's my question;

On the weekend my wife and I had a look at the new Ford XLT Ranger. We both fell in love and considering buying one now towards the end of the year. (Doing my part for FoMoCo)

So simply, for the purpose of towing a heavy load, is a 6 speed auto rated better for the sake of lasting the distance more the a 6 speed manual? Or vise verser? If so, why?

Thanks in advance