You really have to think about the science behind calibrating. You can change a couple settings on a few sensors and the car might run better, But you have to keep asking yourself why did GM add XX table and how does it effect the other tables I didnt change.

Greg's DVD are good and so are the tuning schools.

Dont make a bunch of changes at once. Change 1 or 2 calibrations, then scan again to see the effect.