Be sure the machine is spotless and clean inside, the fans work like new and items like the BIOS is current and drivers are the version that worked before.
CPU drops to 30% when I play games for 8-13 seconds and I am lagging in this time. When the cpu rises to 80-90%, the fps grow back
cpu- amd fx6300
ram- 8 gb ddr3
gpu- rx 470

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic