Even though you have a good download speed (1Mbps), you have not included any information about the the upload speed (the most important).
With this in mind, I recommend you to check this link in order to get further information about this issue and its possible root causes.
I have a slingbox pro and when installed last week it workd great for 2 days. Now, twice the video has frozen for days at a time while the audio still works. I can change channels using the guide, but again only the audio (the video remains frozen on the same frame from 3 days ago.) The remote control does not work either when this happens.
It seems like this is a common problem for a lot of folks, but there doesn't seem to be a clear answer. Pretty dissapointed in Slingbox at this point.