IIS is taking lot of time to deliver first javascript and image file

IIS is taking lot of time to deliver first javascript and image file

We have a Content Management Application and when we did the testing using
a load runner we saw very good performance (pages were rendered less than
2 seconds (most of them in milliseconds).
But now we are monitoring the application with various tools and we
noticed that the first session of the user is taking a lot of time (like
50 seconds) and when we check the first javascript and the first image
loads in about 20 to 30 seconds each. It is always the first javascript
and first image (how small the file size is, I swapped the file order and
see the same behavior) I am not sure where to start the debugging. Any
help where to start the debugging will be highly appricated.
Thanks