My opinion; if you are going to be pulling 14,000 pound trailer (so over 20,000 truck and trailer) you NEED at least an F-350 Dually, PERIOD. An F-250 will very much have the "tail wagging the dog syndrome"..... If NC doesn't penalize you, (for example, Indiana does not, but California does) I would go with an F-450 or even an F-550 with a bed if available. In Cali, anything over a 350 is considered a "commercial vehicle" even if it is for personal use, and has a bed....
I don't think a 250 even is rated for that much weight....... even if it is "rated" to pull that much, it doesn't mean you should pull that much..... I know this from experience. It is on a smaller scale, but the same results. I had a 2000 Dodge Durango with a 5.9, and a 21' Coachmen Travel Trailer that weighed about 5500lbs (about 8500lbs total). This was within the limits set by Dodge, and I had some to spare. I towed this setup for a year and a half. I had the proper setup: brake controller, weight distribution hitch, sway control, and the factory tow package on the truck. One, In that year and a half, I killed the transmission, but in that era, transmissions were not Chryslers strong suit, I averaged about 8 MPG towing (and 13 empty). Any trip was EXHAUSTING, because the entire time we were on the road I was DRIVING. With similar size and weight distribution, you are at 100% all the time, watching, correcting, trying to keep centered in the lane since semi's will push it around. Normally the day we got where we were going, or the day we got home, I was ready for bed.......
In the middle of the second season, I bought my Excursion. The first time I towed with the Excursion, I still had the hitch head adjusted for the Durango. At the time, I didn't store the trailer at the house, so I had to tow it about 5-6 miles "dead ball" (no weight distribution or sway control) to get home to have my tools. The Excursion towed the same camper better "dead ball" than the Durango setup 100%. Now with the setup, the truck weighs about 8000lbs when we travel, and the trailer was still 5500, so more weight total (~13,000lbs) but the truck had much more to "fight back" with........
So if you are going for that big of a camper, big thing is, a 5er tows MUCH BETTER than a bumper tow like I had, but get the MOST TRUCK you can afford. I have decided that for what I do at this point (have flatbed utility trailer, access to a car hauler, and we are looking for another travel trailer <30ft, I will NOT own a truck that is smaller than a 3/4 Ton (F-250, and me Excursion is actually on a 3/4 ton chassis and has 8 lug wheels and a full float rear axle). The wife and I are talking about doing some extensive traveling when I retire, and being on the road a lot, if I don't have a motorhome, the truck WILL be a Dually, PERIOD.
My Dad has a 2012 F-150, and I have my 2003 Excursion, and the F-150 is rated to tow close to what my Excursion will..... F-150 is 7500lbs, the Ex is 11000. But.. if I had to pull a 6500lb trailer... I would use my truck before I used Dads.........