Have you recently repasted your CPU and GPU?
i had the same problem with my laptop GL702vsk. Usually, gpu and cpu are under the temp limit and fps drops to 30fps in games with high GPU utilization(not cpu). I tried repasting cpu and gpu doesn't help. Later i found out that VRM's on motherboard are running hot and not making contact with the laptop heatsink. They don't have a screw to hold it tight so i taped them to hold tight. No performance drop ever since.
haven't you tried to update bios or something else ?