Aluminum chainrings wear faster than steel chainrings. My experience has been that some aluminum chainrings last 10,000 miles and others only 1/3 that far. It can be difficult to tell if a cassette is worn. If you have ridden with a stretched chain very long, chances are the cassette needs replaced. Years ago, I had a cassette skipping and the shop replaced the chain. They thought the cassette look okay. It did not skip until the first steep hill on the Hilly Hundred. The Hilly mechanic replaced the cassette at the first sag stop. I was lucky that he had a cassette on the repair truck. After many years and miles, I have learned that bicycles (especially tandems) are complicated and expensive.