Those CRC errors, as you mentioned earlier are very high for the uptime, whilst the error rate is high, you will see a slow down in throughtput, but if the slowdown is permanent, something else is happening. You are not being capped now because the Noise margin and Sync speeds are not consistent for your line attenuation, the noise margin should be greater for that speed, so something is generating a lot of noise.
I don't suppose the increased error rate coincides with phone use, can you hear any crackling on the line when using the phone? Or do you have a Sky box connected to the phone line (filtered) for interactive use, or even not connected to the line? If so try switching it off. If you have a cordless phone try unplugging it and switch it off (base station as well).
My first thoughts were, have you got another filter and modem/router you can try?
I'd recommend that every time you want to swap any thing around or re-boot, log in to the modem/router interface and Disconnect the session first, then power down the modem/router before unplugging it or the filter from the line. If you are just re-booting leave it off for a few minutes before powering up again. Don't re-boot/resync more than about 5 times in an hour and then leave it for the rest of the day, this should help to stop the DLM thinking you have an unstable connection.
What I'd suggest is next time you feel you must re-boot, swap the filter first (using the method outlined) and see if that makes any difference.
If it continues, try another modem/router. If it still continues plug in at the Test socket.
I have to say that my gut feeling is that it is likely to be the modem/router, but only substitution will prove that one way or another. If you haven't got another, try and borrow one (not locked to another network of course)
