I know it's a long shot, but is it possible the case vents/filters/fans are dirty? This will restrict airflow to cooler meaning warmer air into cooler .. and every degree warmer air is going into cooler is same number of degrees hotter CPU will be. 
What case and case fans do you have .. and what is fan temp to speed curve?

What case and case fans do you have .. and what is fan temp to speed curve?