I am pulling an Evergreen Amped 28FS. It is a little under 10000lbs empty with a max weight of 12900. I am probably at about 12000 most of the time. My truck also has the 4.10 gears like yours. mine is lifted with 35" tires so it is more like the equivalent of 3.73. I can tell that the trailer is there, but it will accelerate up the mountain passes in Washington and maintain the speed limit if I want. If I remember correctly the 5th wheel rating is 13500. In a trailer as heavy as you are thinking the tongue weight would be higher than the factory receiver is rated for. My tongue weight is typically about 1700lbs, but I am using a Torklift receiver.
