I see this page about Slintv:
But I do not see it on the list of supported sites on the DVR page...
Can you provide a detailed description of how to record SlingTV shows?
You should still be able to use the DVR to record from slingtv as described. The sites on the DVR browsers default home page are just suggestions, not a definitive list. Enter slingtv.com in the DVR browsers address bar and go from there.
If you have issues please provide debug logs as per https://support.jaksta.com/discussions/topics/6000009063.