FPS Stuttering and GPU Temps (AMD)

[chibee1]

i have an rx480 and i notice when i play games it will go up to 90 degrees so i would change the Fan speed and Max and target temps in the Global WattMan, but if i do that the temp will go down however my game will stutter a lot every second. However if i keep the Global WattMan default it will not stutter at all and i was wondering how i could fix this and why changing the fan and target temps would cause this.

Rx480 sapphire 8gb
i5 6600k
8gb ddr4 corsair vengeance
600W PSU

 

[ano1337]

Try cleaning it from any dust