Thank you so much for the responses. It doesn't seem to be losing tension, the blade appears to be slipping, but not all the way out, so I can't tell if it is from the bottom or the top. I can tell by the way it cuts that it is loose, so I stop and tighten it before it comes all the way out. I will look closely next time it happens to see if I can tell which is moving.
Thanks so much for the maintenance suggestions. I will definitely implement those and see if that helps. I will let you know what I find out.
Thanks again for your quick responses.