Thanks for all the replies.
Just to clarify--I asked a shop to, among other things, replace both the cassette and the chain about...mmm 5-6 weeks ago. I was still having problems, so, about a week and a half ago I went to a another shop and they said that the chain was not a good one, was worn, and suggested that it be replaced. Even though the chain was only 4-5 weeks old I thought they may have been right because when I wiped the chain with a rag I could feel nicks and burs that caught on the fibers of the rag. I don't know how long a chain should last, but I am riding about 100 miles a week, more some weeks, so that would mean the chain had about 400-500 miles on it. Seems it should last longer than that.
The hanger seems a likely culprit. I've crashed a couple of times.......well, several times.........ok, a bunch, which could have bent it. Also, I've looked at other bikes and talked with other riders and they seem to be handling the dust without any of the issues that I am having.
Thanks again for all the input and offers.