Sorry to hear you are having some video freezing. As you suspected, when video "freezes" it's usually a network speed issue.
We have an article, Slingbox system requirements for HD and SD streaming that outlines some of the minum speeds needed for effective streaming.
Although this article is about the PRO-HD, it's standard definition requirements are similar to the PRO.
You can test you connection speed at sites like speedtest.net to see if you are in range for streaming video.