Why SSIS Package Slower And Slower

hi, friends, please look at this:

I have a SSIS package, and inside it I do something like below:

1. I have a SQL component, to give back a object to store the records.
2. I have a VB script component, I direct the object I got in 1 step into the script as a dataset.


My problem is:
I run the package in the SQL SERVER 2005 Store Procedue like this:

do
dtexec.exe package.dtsx
loop untill i>t

I control the it runs 30 times. But I found that the speed is slower and slower.
the first time, it takes about 600 s, but the last time, it takes the 1800 s.

Why?
The package don't drop the object it create during the loop in the Store Procedue ?
Thanks!