I am having the very same issue on my NY locals in HD only. I have two 622 receivers going through a DP44 Switch. The signal strength on my 61.5 remains constant in the mid 70's. I too thought it might be weather related however it is happening in clear blue skys. I went and checked the LNB connection, removed it and re-tightened - no difference. I called DISH and the CSR too reported no issues with the channels but made a report. A relative who lives 15 miles from me with the same setup is seeing the same exact thing. Could this have anything to do with the L511 Software this past week or so? It is very annoying, more than 8 freezes every 30 minutes on any local HD channel. I want a credit.
I am beginning to think it has something to do with the software upgrade. What bothers me is a few people have contacted Dish, and the CSR's seem not to have any record that multiple people are having the same problem.
They keep telling me I am a valued customer....just not feeling it.