Need Literature Recommendations

What are some recommended readings for playing limit hold'em short-handed and headup besides HEPFAP?

I know of no specific books that really tackle these subjects in-depth. I would recommend theory of poker as a good place to start, even though it is not geared towards these situations. However, if you have a good understanding of theory, you might get some useable ideas. You could also practice heads up against turbo texas holdem, although the usefulness of computer programs is somewhat limited, especially if you are already an advanced, experienced player.

I have Theory of Poker and I have been practicing with Turbo Texas Hold'em. I just think I'm still feeling my way around in the dark.