Its mostly knowing how a diesel works and knowing what each item that makes the engine run. Many make just slight changes to the most common used tables and log it and see what is improved or has lost. Somewhere on here is a link to some books that may help. Use the search tool and search for ' books '. Check out some Duramax Forum sites for possible EFILive help. You can take the tune you have bought and maybe take the tables in quarters and increase the stock tune a quarter to see the differences in slight increments. Good luck

Brian