What's the speed when you write or read from the USB? And what's the speed when you have the USB plugged into your computer directly?
Both USB ports on the C7 are USB 2.0, so that will limit the transfer speed regardless of your drive being 3.0
That aside, I can tell you I've had problems with the original cable that came with the drive as it wouldn't fit tightly into the usb port. I took a chance and bought a new cable online, and that one fit properly.
I didn't really have transfer issues. My problem was that the router would take too long to recognize the drive being plugged, as well as it would often lose connection with it.
In sum: if your drive connects well and responds to 2.0 limitations, then there's nothing wrong with your router. If you still have some bumps in transfer or disconnects, try using a different cable.