There could be a number of reasons why the quality isn't where it's supposed to be. Often, it has something to do with the network connection either where the Slingbox is, or where it is being viewed. I would take a look at this article, as it addresses the majority of these kinds of picture quality issues:
I would also consider rebooting your router and Slingbox at home (unplug the Slingbox, reboot the router, and once the router is up, plug the Slingbox back in). It could just be a simple matter of needing to reboot the system at home.
Hope this is helpful!