I am currently working on a similar issue, the slingbox solo has been working fine for a long time, suddenly the streaming is stuttering and halting. I have checked the internet upload and download speed and both are as good as would be expected.. however the Streaming is still POO.
So tonight i am setting up another slingbox on the connection to diagnose that the upload QUALITY or Throttling is causing the issue..
I have tested over the UK internet and it stutters badly as badly as it does to malaysia where the user works. So I hope to suggest to you to complain to your ISP when I get back OR wether it is possibly a fault on your slingbox.
They can get funny when they overheat for long periods of time.
I shall get back in touch later on.
Actually I meant to ask, how is it over the local Area Network? When you set it up does it set up nice and quickly?? Does your test picture stream ok?
If so then it is most likley to be an issue with the slingbox hardware than network issue. A way to check this for sure is to set a manual IP address on your PC in the same range as the Sling box IP and use a network switch to connect the pc network cable to the Slingbox.
If it can not stream over a LAN connection it is fair to assume the sling box is faulty.
IF you want help to set a manual ip address for your pc you can google for it or let me know what system you are running,, windows osx etc and I can offer some advice... Also a 4 port network switch shouldnt cost more than £10 GBP. You can pay more but they are a cheap bit of kit.. this is a legacy connection and will rule out firewall issues or network nonsence in your router... its the same as a straight connection of the LAN cable to your slingbox.... which you may be able to do with a crossover network cable and manual ip's.. I think I have waffled enough..
I have a similar problem. It happened after I added a second D-Link DAP-2553 access point to my local network. The access points are set up as both access points and bridge. The computer behind the second Dap-2553 will find the sling box but will only stream at about 60.
IS there a possible setting in the access points that the slingbox does not like? Up until this change it has worked flawlessly over my local wireless/wired network.