You probably won't gain any hp right off the bat, unless your experensing false knock that the 99's are prone too.
Are you putting in 02' injectors also? If not you might run a little lean because the pcm is programed for 24 lb injectors where the 99's have only 19 lb injectors.

Also they contain more memory as well which probably is because they have more options for programming. Something about the timing tables are better rings a bell too.