hd channels intermitent service interuption

For about 3 Weeks now a handful of hd channels dont come in while the same channels in non hd broadcast fine. I have had 3techs out at my home and the latest tech put yesterday was a high level tech. Couldn't really find any problems made a couple of modifications and left, was working fine until this morning. Should note that out only effects 5 hd channels, its always the same 5 and it only is doing this on 1 cable box. Today the outage of those channels is running about 1 hour the longest ever. It effects dvr recordings because out shows no picture so it records nothing. Any suggestions. This problem is baffling everyone.c