If trying to stream in HD, try turning off the Video Data Saver to see if your buffering issue is solved. Keep in mind that streaming in HD can, and will, use a LOT of data, though you are in a relaxed bandwidth period during your first twenty days of service, so your data allotment keeps refilling during this time.
Just keep that in mind, as if you are doing a lot of data intensive things, like streaming in HD, you won't be able to do nearly as much of such when the relaxed bandwidth period ends, as you could run out of data very quickly.
Edit: To test your speed, you should use testmy.net, and use the manual 25MB test size for download tests and the manual 4MB test size for upload tests. If testing for troubleshooting purposes, you should test with a single device connected directly to the HT2000W modem with a LAN cable, and with the HT2000W's WiFi disabled.
See "How do I manage my built-in Wi-Fi modem" in this PDF for instructions on disabling the HT2000W's WiFi.
The proverbial poo will hit the fan come day 21 if you think HD streaming is a good thing on capped satellite plans. I don't do it even with a 50/50 GB plan.