You will arrive at D terminal, the international terminal at DFW. UA flies out of E terminal. There is a SkyLink train that goes between the terminals, the problem is that it's airside.
I've never done Intl-Dom at DFW, used to live there and terminated/started a lot of trips there. I'd say it's best if you make sure you stay airside, otherwise you'll have to go out into the blast furnace that is Texas in the summer, get on a shuttle, and go between terminals that way.