answer:Sounds like you do put a lot of wear & tear on the thing. If you’re averaging 80 mi./week for 50 weeks of the year, that’s 4,000 miles you’ve logged. Chains do indeed stretch and need to be replaced regularly. Cassettes and the big sprockets up front can have their teeth worn down, especially if the chain is ill-fitting. So it’s certainly possible that replacement there is warranted, too. Find a shop you can trust. Keep receipts of the work done. In my experience, the repair of a single item might need multiple visits to allow the mechanic to get everything dialed in just right. Especially around shifting, as cables stretch, need proper tension, and derailleurs need to be aligned just so, etc.