X1 picture quality issue

I have an on going issue with picture quality, sometimes the picture is good, resolution is sharp and crisp and sometimes the picture quality is low res and I know its not related to to the original picture or signal.  It does seem to be better during off hours or low demand hours.  Is there a way to check signal strength, I have heard that Xfinity hasn't updated their infrastructure in older neighborhoods. Could I have an issue with old infrastructure and how do I get Comcast to update my infrastructure. I have been a long time customer paying for premium services but not getting a premium picture.  Does anyone have a similar issue and suggestions for getting it resolved.