How do I tell if a device is doing USB 3.0 and not downgraded to USB 2.0 for some reason?
Try  menu &gt;  About this Mac &gt; System Report...
Select USB on the left, then find your device in the list.
The reported speed ought to be a giveaway. Mine shows it's only running at USB2 speeds [but that's because I don't have a USB3 machine]

List of speeds &amp; common names…
USB 1.0 / Low-Speed: 1.5 Megabits per second (Mbps)
USB 1.1 / Full-Speed: 12 Mbps.
USB 2.0 / Hi-Speed: 480 Mbps.
USB 3.0 / SuperSpeed: 5 Gbps.
USB 3.1 / SuperSpeed: 10 Gbps.