Please check the home speeds of the network you are using with these unit. You can do this at speedtest.net. Use the article below to confirm you are meeting the minimum requirements for the Slingbox 350. An upload speed of 2.0mbps is required for your unit to obtain best quality possible. If you have an inefficient upload speed could very easily cause the issue you are describing. Have you tried to factory reset these unit? Listed below are some article to help you troubleshoot your issue. Sounds to me like a network speed issue via your post.
Sling Media Technical Support