Sorry to both you, FurryNutz, but I was able to solve the problem by disabling automatic uplink in QoS.
FWIW, the automatic uplink has a maximum of 2048 kbps and the ISP I subscribe to gives more than 3,000, so I just set the uplink manually to the max.
Finally, it's a problem that's probably dependent on region, ISP service, etc.