Another last try from me was exchanging sim card with a friend from the same cell provider. Mine was prepaid and his was postpaid with extra charge on billing bla bla bla. I saw a big difference between mine and his especially when our two Bolds started and tried to find signals. The prepaid was slower then the postpaid sim card. When the prepaid still reach GSM, the postpaid reached GPRS and EDGE. And when the prepaid still reached GPRS, the postpaid had reached full 3G with Blackberry mark on it.
Then I made another conlusion: could the hotness of the handset caused by the long and heavy effort to find signal? I don't know about your providers in America or Canada, but in Indonesia I found that there is a big service difference between postpaid and prepaid sim card. Maybe it was not 100 percent of the answer of why a Bold got hot in a very short time while other Bold can be very cool even after heavy abused. May be it's 50 percent cellular service problem and 50 percent hardware problem. I don't know. But from my experience, I know that the cellular service had something to do with this problem. So maybe you can try to exchange sim card with a friend with THE SAME CELLULAR PROVIDER and see the result when your two Bolds starts and works together at the same time. Is your used-to-be-hot-Bold not hot anymore after using your friend sim card or what.
I also wonder if there any real Bold technician who can also give opinion to this "hot" matters since I read all opinions came from end user only.
But still I really really think this is all hardware problem: the inability to find signal or receiver or something like that.