4870x2 Overheating

I've got a Sapphire Radeon 4870x2 and it's not OCed. I was playing Rainbow Six Vegas 2 a week ago and I heard my fan kick up to like 80% roughly. I alt+tab to check the temps and it was running 93C. I've never had it that hot before. I live in Arizona and even over the summer, when I got it in August, it wasn't capping that hot. I cleaned it out today (along with my Antec 1200 case) with compressed air and plugged it back in. I ran the game again and it STILL overheats. Now I am worried the heatsink is not fastened well enough. Idle temps range from 55-62C at a 50% fan speed, which is unacceptable, especially for this case. My question is, do I void the warranty and fasten the screws tighter on the heatsink, do I get a custom heatsink, or do I RMA, or, am I missing something?

Windows XP SP3
Intel Q9550 OCed at 3.2Ghz
4GB AData PC2 6400 RAM
Sapphire ATI Radeon 4870x2 not OCed
640GB WD Caviar SATA HD
SoundBlaster X-Fi Xtreme Gamer
Kingwin 1000W PSU Silver

I also have a 120mm side fan blowing on the card