if your at 28°C under load it shouldn't even get close to 55°C that was more of a Max temp I would allow during testing, on the off chance you had poor case ventalation, or sitting on the equator. I should have specified that. (AMD says Max is 75°C I've been up to 65°C during over clock stress tests)
I think CPUZ is having issue uses with the voltage reading. stock is 1.375 I believe and AMD says 1.4V Max. you are essentially turning it into an X4 though, which has a higher range.... something else that might cause that error an unstable power supply having voltage fluctuations, or the motherboard doing a poor job of regulating the voltage. that could also explain the voltage CPUZ is seeing. is it stable in prime95 without trying to unlock it?