Yea its not to good to have that many uncorrectables. Have you been checking the levels on the modem to see if they swing 12db still? What is the level on the cable box now . Is there any amp in your house? If the signal on the box/tivo remained the same and modem signal changed then you have a issue with that splitter leg or wire or connector.
Sometimes if there is a piece of cable shield braiding touching or near center conductor in connector it can cause signal to short out or levels to fluxuate , it will also give you corr/uncorr.