What happens if you miss connecting flights.?

You do not need to go through immigration to exit the United States. Even if you are flying from another country through the US and on to Guatemala, you will only be in transit, you will not actually enter the US, so no immigration. Another important information you did not provide is: which airline are you flying to Guatemala? If it's also AA, then you should call AA and let them know so they can link the two separate tickets in their computer system. Even if it is not AA, it may be possible for you to check in all the way to Guatemala if the other airline is an AA partner. In my experience, 2 hours connection time is adequate if you don't need to take your baggage out at DFW. In any case, let both airlines know your full itinerary. Ask the agent on the phone to type in a note in your record. It will be to your advantage if something goes wrong.