I cannot get to various HD channel or they are so bad they are unusable

This along with extremely slow Guide navigation and channel selection has been happening for DAYS.  Reboot/refresh does no good.  It is NOT a subscription or cable connection issue. Guide issue magically better today but HD issues remain.  We have had similar issues in the past for a day or two but this has been going on almost a week.  Getting quite tired of paying for consistently unreliable cable.