I think you are cutting it awfully close. You will not have to recheck bags, and getting through transit security is usually not a long process so long as you have a printed boarding pass or at least a printed intinerary for your ongoing flight. However, getting to transit security and then your next gate can take some time.

Terminal 2 has two concourses connected by a train. Both AA and CX are in Terminal 2, so that is good. But each concourse is very long. AA flights use both concourses. So if you come in at Gate 77 and depart at Gate 97, for example, it is going to be a very long walk and plus a short 2 minute train ride (but you might have to wait 4 or 5 minutes for the train).

Another factor which is always a wild card at Narita is which runway you land on and in which direction. One end of the second runway that opened several years ago is near Terminal 2 but the other end is completely away from the airport. Most inbound AA flights use this runway. If you land going away from the airport, the taxi back can take a long time as you wind your way back along side farms that Narita was not able to obtain for the airport expansion. You will even see "Down with Narita" signs posted on the farmer's fences. It is a curvey and slow taxi back......but interesting to see how much clout Japanese farmers have. You can be wheels down 5 minutes before scheduled arrival but be 15 minutes late to the gate.

Another observation after taking more than 75 flights to NRT over the years is that it takes what seems like forever for the GA to get the jet bridge to the aircraft door and then open the door. Much longer than what it takes at most US airports.

Add it all up, and I think you are cutting it pretty close. You only have 40 minutes from scheduled arrival until boarding of your next flight as it is. But you are on the earlier flight from DFW to NRT already, so there is probably not much you can do except hope you arrive at the gate on time and your gates are not a mile apart. If that is the case, you will be fine. The transit security process iteself is well marked and easy to do and is pretty fast (but don't forget the printed boarding pass or intinerary).