I understand that you are experiencing speed issues. We need to get more details about this situation that you have right now; do you have this only remotely or at the Slingbox location too? Meanwhile, have a look at this article:
If you only experience this behavior when you connect to the Slingbox remotely, probably the cause of this has to do something with the upload speed at home or a network restriction:
Have you tried to perform a power cycle at home? Take a look and perform the step #2 that you will find here.