Overall a 3 year old PSU used for heavy gaming is prime suspect:
You have a number of troubleshooting options:
Look in Reliability History for error codes, warnings, and even informational events that correspond with the restarts. Increasing numbers of errors and/or varying errors are symptomatic of a failing/faltering PSU. The PSU may simply no longer be able to meet current peak power demands under some conditions.
Reduce the number of programs running in the background. (Side note: I am curious about why an uninstaller is being continually left open? Not a criticism - just a question.)
Use Task Manager and Resource Monitor to observe system performance and determine all that is actually running. Use both tools but only one at a time. Do not randomly start disabling apps, etc.. Focus on what is running and why it is running. Good chance that overtime more programs are being launched at startup than you realize. Process Explorer and Task Scheduler are likely to prove helpful.
Lastly hardware:
Power down, unplug, open the case.
Clean out dust and debris.
Check by sight and feel that all connections, card, RAM, and jumpers are fully and firmly in place.
If the problems continue then the next step is to test the PSU. You will need a multi-meter and know how to use it. Or have a family member or friend who does.
Recommended reading:
https://www.lifewire.com/how-to-manually-test-a-power-supply-with-a-multimeter-2626158