Why are my fans doing so little to lower heat?

I recently did an install of a new I/O board on my MacBook Pro due to a bad Magsafe connector. After starting up my computer, I noticed it was running a few degrees hotter then it previously had. About an hour later, while idling, the fans kicked into high gear and iStat Pro showed them as running at max speed (6200 RPM). I figured it was because it was warm and dismissed it. After the CPU temperature came back down to around 50 C, however, the fans did not spin down like they should, I waited about 30 minutes before turning off my laptop just to be safe.

Now today I was watching a Flash video (which I realize is very CPU intensive) and my CPU temp went up to 75 C, and still climbing while the fans ran full power. I've had this laptop for 3 years and never had an issue with heat. Is it possible that a temperature sensor was damaged during the install of the I/O board? Did I go anywhere near the sensors? I'm not even sure where they are, to be honest. I wish I could run the AHT, but I've lost the DVD that came with my computer (I blame the frequent moves on this). Is there any other way to figure out what the problem could be? I guess if this rambling is a bit unclear, I'm wondering why the fans are spinning so high when nothing is happening, and at the same time doing very little to actually cool the computer.

Thanks.