I have been having the exact same problems as you since about a week ago. Online gaming has become impossible, when ringing CS they just say we can't see any problems sir. And due to both sync and rdy lights being solid they quite simply state it's a problem with my pc, which I know for a fact is not true. When I reboot the modem, it seems to get a better upstream signal but this only lasts an hour or so, then my connection goes back to "normal".
It seems that it's definitely a problem with upstream, packet loss has been as high as 68.4% on some days when tracert'ing
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