In some cases, even where there is plenty of upload speed in the speed tests, we find that a client's router is throttling the bandwidth due to settings in the router. If you search for your router name/model in Google with "QoS" (for quality of service), or search for your router name/model with "priority", or browse around in your router's settings, you can see if there are any places where you can increase the allowance for streaming priority or upload speed in general. In various support calls we have found this type of setting causing the connection speed issues (it may not be the case for you, but it may be worth reviewing). Below is a link to a basic article on the subject as well as a link to a setting for a Netgear router as an example.
Also, if you know the make/model of your router, please feel free to provide us the make/model via a support ticket and we can research it a bit.