What kind of numbers show for the RxSNR, cable resistance and Cable Attenuation on the modem status page? Are there any red flags on the status pages for modem and tria? To see the modem status, plug in this address in your browser: http://192.168.100.1/?page=modemStatus
I'm sure you checked already but also be sure to check your router...ours recently drug us down to speeds that weren't usable at all. Once we bypassed the router speeds were "normal" so we had to troubleshoot and adjust the router. At that time, even rebooting the modem and the router wasn't working it kept dragging the speeds down. Hope you resolve it soon.