Sounds like a problem with your source. I'm not saying anything is broken, but from your description the Slingbox appears to be working normally. I suggest you start by verifying what your source is feeding the Slingbox.
Streaming at a low speed like what you mentioned is normal if the image being sent is very simple with no motion... like a black screen. As soon as image complexity increases, so will streaming throughput.
That said, I would expect the Weak or No Video Signal Detected message and possibly even slower streaming rates if the source was sending absolutely nothing and/or the Slingbox wasn't processing a video feed. As it stands from your description, I think the source is sending a signal and the Slingbox is encoding/transmitting it. It just happens to be a blank, black frame.
A few things to try and check:
- Are you sure SlingPlayer is set to the correct input ? It probably is, but doesn't hurt to check. In Slingbox > Video Input you can flip between Composite and S-Video for your Slingbox AV.
- Are you getting audio ?
- Are you using HDMI anywhere else in the overall equipment loop ?
- Try using a TV to check the same source, cables and connection type. Any changes ?
Any other details or clues you can share might be helpful.
Hope this helps,