What is the drill mod? What are its advantages? How is it done? What is an adjustable master cylinder?

The reasons for these questions is I have had shifting problems in my 01 pickup (race mode) and I have felt like the slave cylinder was not acting quick enough or the clutch was not disengageing quick enough. I am in the process of installing an LS1 / T56 and would like to make sure I don't have the same problems with it.