Well here is my 2 cents worth of information on this topic. I have a 2005 Expedition with the 5.4 4x4 and tow my boat and my 4 place snowmobile trailer with it all the time. I purchased the boat in California and I had to go down and pick it up. Now I live in Utah so the drive home was pretty much all up hill. It did a great job on the 900 mile trip home and really surprised me on how well it did. Here in Utah I pull our boat to Bear Lake which is about 2 hours from my home a couple times a month which I have to go over to passes to get there, no problem. The real issue I see when pulling is when I get behind someone that is going slow up a hill. Recovery is not there like it would be with a diesel motor, or even a bigger motor. Overall for what we use it for I can't complain a bit. This is our 2 one and have pulled many trailers and boats all year around.
Hope this helps.
My boat is a 2006 Sky Supreme V232.