Jim Taggart, along with most the looters, are in a constant battle of self-contradiction. We learn from Hugh Akston that contradictions don't exist. Yet Jim and the others try to live with their contradiction of wanting to strangle everything superior and good while at the same time wanting the superior and good people to go on producing so they don't starve.
Therefore, Jim cannot be tipped off by his own contradictions nor his rising insanity. He's aware of it already, but constantly hides it deep down so he doesn't have to confront it. When, after the torture of John Galt, Jim is finally forced to confront his contradiction and insanity, his mind implodes, and he is never the same again.