SteveS said:1 Somewhere N/E past the 121/Custer intersection.
...As to exactly where, we don't know. (LE may have better info on this.)
...It is my belief they went to "get something" and it was together (ie, with her as a passenger). Quick cup of coffee, so she could wake up for her drive to FW? Some drug, for the same purpose? Some drug, for a diff purpose? Just guesses.
2 My speculation is that he was taking her back to her car, after they went together to Place X. Both "where did they go" and "why did they come back" fit together easily with one not-unlikely explanation.
I know we don't know or we would know. lol!
I wonder if near Custer is nearby anything else. Or, is the area just open space and road/s?
We've discussed this at length before, but you may have missed it. Some of the salient info...
1 121 is a tollway with limited entrance and access
2 We know EA went past (not "to") Custer per the toll records.
3 He may have gone to the very next exit, or continued "forever" (within the time limitations) since Custer was the last toll-taking location for an eastbound vehicle (which he was).
4 There are residences, business, all sorts of industry, and more in the general area "past 121/Custer" yet within the time limits. It's growing, suburban, some rural spots, US 75 (Central Exwy to Dallas) not far dead ahead, and you can probably speculate any general type of destination and it's not impossible.
5 LE could have much more ping info for EA during this time and are keeping that info under wraps for now.