Fitness Swimming (Fitness Spectrum S.), Human Kinetics by Emmett Hines is another book I found useful.
Its based around TI principles, but has one cracking image to visualise; the screwdriver.Basically, the power to your stroke comes from your hips, and not at al from your arms.
Whether you follow TI or not,and as I've said, I only used it in (a small) part to learn how to swim myself, this is the thing that you have to learn to understand.Your arms dont propel you through the water as such.
I always found this very counter intuitive, and sped away like a wild windmill trying to get faster.Once I learned to slow it all down, to concentrate in long strokes, not fast strokes, then I found myself going MUCH faster and longer, by a long, long, margin.