Many thanks for the suggestions. I tried the WMM change but it did not help. I do have another router so that will be my next step.
I did find today that all is fine until I first access the DVR/cameras from the network. The first thing I notice is that I can do a Google search and get results but selecting the end target times out. Gets worse until after another few minutes I cannot get the Google site and even access to the router is very slow. Unplugging the DVR-router cable gets everything back to normal in a few minutes. A switch between the 2 units did not help.
If I ever get this working I'll update this post.