Frank, somewhere on your truck wil be a data plate giving a GCWR. This is Gross Combined Weight Rating. What you want is to have a GCWR that meets or exceeds your loaded trailer's weight and the loaded truck weight including the people in the truck. I honestly believe you might want to look at a slightly heftier duty truck than the 350. Sorry, but I would only use the gasser for moving it around the yard.
I agree with you about the gasser.
Yea, I had all the manuals out today, it was too cold to do anything else, and I found it a little bit confusing trying to work out what you could actually pull on a gooseneck. I reckon if it is rated to pull 10K on the rear, it should surely be rated to pull 14K on a 5th wheel hitch. Just my opinion. But, having said that, if you follow all the instructions for calculating allowable towing weight, you're right, it's pretty darned close for my dually 4x4.
We're going to make a few short trips when we get it home just to check it out. The destinations are all within about 10 miles of the house or the farm. We'll see how that goes. Good Lord, I hope I don't have to drop another $70K on an upgraded tow vehicle. I may have to sell the house and live in the freekin' thing.