9600k poor performance

[PiperWarriorFlyer]

Hello.  I have a core i5-9600k.  I've had it overclocked for the 2 years that I've had it, but it suddenly will not overclock over 4.3GHz, and whenever I run a stress test (Prime95 and OCCT), 2 cores throttle themselves back to a load of around 5%, when they're only around 60C.  Many games are performing noticeably worse, and I'm not sure what to do.
Here is the rest of my system:

Board: Z390M Gaming Edge AC

RAM: 32GB @ 3200MHz

GPU: RTX 3070 

PSU: 750W 80+ Gold

[Maria_R_Intel]

Hello PiperWarriorFlyer,

Thank you for posting on the Intel* Community.

Keep in mind that altering clock frequency or voltage may damage or reduce the useful life of the Intel unit and other components, it could also affect the system stability and performance. So we do not recommend overclocking. Also, you have been overclocking the processor for a long time, and there chances that now your processor is not working as expected due to this.

We would like to check some reports, please attach the results:

Intel Diagnostic Tool

• You can test your Intel unit using our Intel Processor Diagnostic Tool (IPDT) which checks brand identification, verifies the processor operating frequency, tests processor-specific features, and performs a stress test on the processor.

Intel® System Support Utility (Intel® SSU) 

• Download the Intel SSU https://downloadcenter.intel.com/download/25293/Intel-System-Support-Utility-for-Windows-
• Open the application and select "Everything" click on "Scan" to see the system and device information. By default, Intel® SSU will take you to the "Summary View". 
• Click on the menu where it says "Summary" to change to "Detailed View". 
• To save your scan, click on "Next", then "Save". 

Best regards,

Maria R.

Intel Customer Support Technician

[PiperWarriorFlyer]

After testing, everything passed both on a base clock and on an overclock.                                      

[Maria_R_Intel]

Hello PiperWarriorFlyer,

Awesome! If the processor passed the IPDT test we can say that it is working properly. We can also check your system information and provide you with recommendations if you attach the SSU and IPDT results to the thread.

Best regards,

Maria R.

Intel Customer Support Technician

[Maria_R_Intel]

Hello PiperWarriorFlyer,

Were you able to check the previous post?

Let me know if you need more assistance.

Best regards, 

Maria R.  

Intel Customer Support Technician 

[Maria_R_Intel]

Hello PiperWarriorFlyer,

We have not heard back from you, so we will close this thread. If you need any additional information, please submit a new question as this thread will no longer be monitored.

Best regards, 

Maria R.  

Intel Customer Support Technician