i have a p55-ud3 mobo, when i am transferring files from one partition to another , or from hdd to usb , tmpin2 goes as high as 89c, although it idles @ 32c when finished transferring, cpu(i5-760) cores reach 47c at highest, hdd reach 39c highest , so it is not cpu temp or bad sensor because it idles normally.
I'm actually pretty sceptical that it's hitting 89 degrees. It should heat up but not that much.
Thermal diodes are notorious for being wonky and since there's no standard way to properly report temperatures to the operating system or monitoring software a lot of generic software such as CPUID will misreport motherboard temperatures. If you're concerned (and you probably should be) you should call Gigabyte and see what monitoring software they recommend you use.