The tyre tracks in the settled dusk seems the confirm the thought that the Mallers section from the end of chapter 24 was in fact later then the start of chapter 25.

While it is silly that Kelly and Pegs were giggling when they met the other survivors at Fort Irwin, remember that the last 1 or 2 days (plus the preeceeding weeks) for them has been really intense. They have been pinning their hopes on there being people when they got to the fort, and there are. Also, I am assuming that their first thought is really that they don't have to think for a while and that might be 'safe' here at the army base. I am not sure how I would react in a situation the same, but aside from Kelly's entry to the tower, both are quite friendly and based on what they have seen from our army boys might be expecting something similar with these guys.

Or shock has finally turned them crazy.