I agree with RR, its probably either (or a combination of) your fan slowing down from age / dust or crud on the shaft, or the thermal paste has dried up and pulled away and you no longer have good contact on 100% of your heatsink to the GPU. The hotter it runs, the more likely you need new thermal paste. 70C is pretty darn hot. Mine runs that hot too, I needed new Arctic Silver after only 1 year. I really could use a better heatsink setup though. The stock one stinks.