So if I understand correctly, you are having problems with your video lagging? It does sound like Internet viewing can be the issue, but before that I would try this, Troubleshooting choppy video in Watch on Slingbox.com.
If that still does not solve your issue, then I would make sure Internet viewing is completed. To complete this just go to Slingbox set up, and set up Internet viewing.
Best of luck and hope this helps,
Sling Moderation Team