That "max tow weight" is based off of the factories listed curb weight for your particular model/engine/tranny/rear end combo subtracted from it's GCWR.....
So, unless you are driving in a stripped down 'work truck' and you weigh about #150 and don't put anything else in the truck, you can tow that much.........
Well, actually, your truck will physically tow that no matter how much it weighs. It'll physically tow #10,000 too, but it won't last too long.......
Figure that #4085 DRY weight for the trailer will grow a good #1000 (or more) once you add some options to it and pack it up. That's usually the weight of the trailer as it left the assembly line. It gets a lot more 'stuff' added to it after and even after it ends up at the dealer.
To give you some perspective, I tow a 22' #4500 soaking wet travel trailer (that's packed and ready to camp). I have the 5.4 and 3.55 gears too. It's a very comfortable tow, but I could not imagine towing it with any less engine and still feel comfortable doing it.
It works going up hills, but I can usually keep it in third. It will drop into second if the grade is long and 5% or more. I have the e40d tranny and tow with OD OFF for the most part. I also have a tranny temp gauge and it runs at about 150* on level ground, but goes up to 180* on the long hills.
The tranny is usually the weakest link in most towing situations. It hates heat, and the heavier the trailer, the more heat it produces.
IMO a V6 is just not enough to tow the trailer you are considering.