As I understand, the streaming rate on your Slingbox fluctuates between 8000 Kbps to 500 Kbps. The issue might be caused by the Internet connection that you are using for the Slingbox.
We need you to provide further information about this issue.
How is your Slingbox connected to the router?
Are you using SlingLinks or an Ethernet cable?
Do you have the same issue on different computers?
Which is the make and model of your router?
Make sure to provide as many details as possible, this way other Forum users will be able to help you with accurate information.