some of the passport / other self powered UBB3 drives aren't particularly fast - although faster than the usb2 disks. There is still an issue with Native usb 3 drivers for windows 8 -- maybe latest version of 8.1 might have fixed these.
Note also a lot of mobos that don't have native USB3 ports won't give you very fast usb3 speed with a pci extension card - bus speed isn't fast enough for true usb3 speed.
New laptops fitted with usb3 ports should provide full usb3 speed provided your device can handle it.
Note it's possible that your "Slow" usb 3 port is not a "powered one". Otherwise sounds like a defect - all 4 should have the same characteristics unless the manual says the spec is different.