Personally I would much rather be booked on the 4:50p flight. You must have some bad luck, as usually 105 mins is plenty of time at DFW to clear immigration, customs, etc. As long as it departs on time NRT-DFW will arrive early often, especially in the winter. I flew it back last week and our flight time was only 10:45.

Worst case if you were to miss the 4:50p flight AA will just rebook you to the later one. As it sits now you have a 5 hr 40 min layover at DFW, which will totally stink as your last connection coming all the way from BKK.