Hello @Beholster ,

Welcome to our community.

For the DSL Line Quality and CRC Errors:
1. Enable SRA (Seamless Rate Adaptation): Log in to your router's management page via tplinkmodem.net, go to Advanced > Network > DSL Settings, and enable SRA. This can help stabilize the connection.
2. Remove DSL splitters or filters: If you're using any DSL splitters or filters, remove them and connect the router directly to the front wall socket to reduce interference.
3. Replace the DSL cable: Try a different DSL cable to rule out cable damage, as faulty cables are a common cause of CRC errors.

For the Speed drops:
1. Log in to the web-based interface of your modem and check the Status page and DSL Status section.
2. Connect only one device to the modem via Ethernet cable and run three speed tests without any high-bandwidth activities (like downloads). Document the results.
3. Check your wired link speed. You can refer to this guide: How to check the associated/link speed on a wired client
4. Change your DNS to Google Public DNS (8.8.8.8 and 8.8.4.4) for better reliability. Guide: How to Change DNS Server Settings on a TP-Link Wireless Router or DSL Modem Router

For the Disconnection:
1. Power cycle: Restart your modem router completely.
2. Hard reset: If the issue persists, perform a factory reset by pressing the reset button for 7-10 seconds while the device is powered on, then reconfigure it.
3. Test with old modem: Since you mentioned you can't test with a new router, if you still have your old DSL modem, try connecting it to verify whether this is an ISP line issue or a router hardware issue.

Important Note: The extremely high CRC error count typically indicates physical line issues, damaged infrastructure, or problems at the exchange. It is recommended continuing to push your ISP to investigate the line quality, as they may need to send a technician to check the physical line.