Why is my GPU suddenly running so hot?

I have an XFX Nvidia 8600 GTS that I bought overclocked at 730. A few months ago I had been playing TF2 with no problems. I didn't touch my comp for over 4 months and noticed this would happen. The game would randomly crash and sometimes my screen would become pixelated until I made a hard reboot. I ran some temp. tests and it is now idling at 73C and runs at 81-83C while playing TF2. I haven't made any graphical change to the game, changed comp cases, haven't moved my pc's location, and never reapplied thermal compound I was wondering if anyone has any idea what could be wrong? Would reapplying thermal paste cool my gpu? Do I need a new GPU?