They might be brushing you off because you are looking for a truck that doesnt exist in any great volume which means that they are gonna have to spend time searching on the computer to find the truck, call that dealership to see if they are willing to trade, try to see if you have a vehicle in your inventory that they are willing to take back in trade.
More than likely, they would be more interested if you were willing to buy something that they have in stock and can make a sale right away. Some salesman can't see the long term benefits of establishing a customer base which takes years to cultivate and this sometimes means that a sale will be a couple of months away vs. a sale being made today. It also might be the dealer's mentality that is a sales can't be made today, then you're not as high up on the important customer list.
The Ford dealership that I pass every day is the 5th largest in the country, and I have only seen one max trailer tow package F-150 on their lot, and it was traded in from another store. Basically what I'm saying is that you're probably gonna have to settle on a non max tow, or order a 2014 model