I understand that you are having an issue with maintaining a stable connection to your Slingbox since you upgraded your router. Unfortunately, the information provided is not clear enough in order to give a straight answer. The main question is whether or not the new router is at the Slingbox location or your remote location.
If the new router is at the Slingbox location, I would recommend a hard reset of the Slingbox as well as a fresh set up. Here is are some links with instructions on how to perform the hard reset as well as reconfigure the unit:
If the new router is at your remote location, the issue may be due to a firewall setting on the router itself. You may want refer to your router's user manual for instructions on how to lower these settings.
Hope this helps!
Sling Media Forum Moderation Team