If you have Gen5 and you are trying to stream in a higher definition, make sure to turn OFF the Video Data Saver. You can do so from the Usage Meter, or you can sign in at http://my.hughesnet.com/myaccount and turn it OFF there (it's under Settings). The Video Data Saver is designed to throttle the speed when streaming to save data, and the default setting is ON.
With that said, it's best to have your Netflix definition set to either Standard, or even Low Defintion, as High Definition uses a LOT of data. I'm not familiar with the settings of Amazon Video, HBO streaming or Vudu streaming, but if you are able to adjust them, it would be best to set them to Standard or even Low Def, as, again, streaming in Hi Def uses a LOT of data.
But, if that doesn't seem to make any difference, or that is not the issue, and you are streaming with WiFi, try streaming on something that is directly connected to the Hughesnet modem with a LAN cable to see if there is any difference. It would also be best to, during this test, turn everything else that uses Hughesnet off, or make sure they are already off, so that nothing else is utilizing the bandwidth. Only the device you are using for the test streaming should be using the service at that time.