Hi @mahr0z
What thermal paste did you use, some factors I would check,
had you tried upgrading the computer BIOS?
you can use the service tag to search for the computer updated bios
https://www.dell.com/support/home/sg/en/sgbsd1?~ck=mn
check @ task manager…. see what is causing like cpu percentage going up.
sometimes bad graphic card drivers may also cause this, try to update those to latest, and others, like chipset, etc.
and background software, e.g. antivirus….
check on the internal fan, even if it is clean, inspect that it is running well, e.g. no resistance or slow.
you will need to power off and one way I test is using finger to spin the blade. it should not have resistance and spin in a couple of times before it stops.