A sharp drop in FPS in games.

Greetings,
There is the Asus k551l. Worked fine for 2 years. From time to time used it for games. In the last two months faced with the fact that the game is showing a sufficient number of FPS became after a certain time to slow down. Play itself and there is a reduction in performance several times. It is clear that the problem is overheating. Cleaning from dust, thermal paste, all that stuff. Disassembled the laptop, saw a minimal amount of dust-removed, removed the cooling system-I saw a minimal amount of thermal paste - removed, caused a new (thin (~0.5 mm) uniform layer. It did not help. After a certain amount of time depending on the game, fps drops. Checked the system for trolling through the software. Software loaded CPU, the temperature rose, but the drop frequency is not observed. Temperature of kernels in idle (HWMonitor) + -45C that much in games to 75C, the temperature of the video has similar results. What can you recommend?