There are a couple of things to do when we see issues like that, however, before we go through any of those other steps, I would first ask you to run a test on internethealthtest.org while the SlingPlayer is running. This is a website setup by the FCC to report potential throttling on networks as this is no longer allowed via the Net Neutrality laws. Take a look at how the Consistency and Highest/Lowest speeds fall and let us know what this looks like.
I hope this helps!!