Details can be found on this link:
http://weblogs.asp.net/bleroy/archive/2008/06/12/script-reference-profiler.aspx
Watct viedo for using it:
http://www.asp.net/aspnet-in-net-35-sp1/videos/using-script-combining-to-improve-ajax-performance
Add below to page to find the running scripts
run the page again and it will show all the scripts that take time collect them and paste then in