A glance at his splits this year show a few interesting things.
He's hitting .432 in the first 2 innings. (37 AB's)
He's hitting .440 the first time he faces the SP.
In 10 day games, he's hitting .270 .356 .324, with both his doubles, 4 RBI and 5 BB.
While he is hitting a lot of groundballs, his average on them is .292.
In my opinion, this shows that Jeter has two potential problems. One is that he loses energy early in the game. I doubt that's it. The other and most obvious problem is that his eyesight is giving him problems. He's hitting better in day games, and early in night games. As the natural light diminishes, so does his ability to hit.
Most players have problems at age 32, Jeter's seem to have started last year at age 36. If I was in Yankee management, I'd be sending him to the best eye doctor in town.