If you have a Dell computer, and Dell Optimizer is running, if can limit the network bandwidth trying to prioritise some apps.
You can run it by clicking on the Windows icon and starting to type Dell Optimizer, it should show up. Then disable network optimization.
Thanks! This just fixed my issue. It made no sense why this was happening and to make matters worse I was getting conflicting results between Fast.com and Speedtest using the same browser so it wasn't even application specific. It almost seems like Dell's Optimizer software is restricting speed to certain sites rather than at an application level.
Typically I uninstall all bloat when I buy a new comp but was kind of lazy with this one.....eh guess I learned my lesson.