the x4 b55 runs fine and is stable all day on prime95 but it seems to be throttling the core speed and multiplier during the test, going from 3310 mhz x16 to 880mhz x4, the cpu temp never reaches over 43 degrees Celsius and the fan speeds are low, i turned off the amd cool and quiet and that makes no difference
when the chip isn't unlocked and is a standard x3 455 on prime i get a max temp of 66 degrees, fans run at higher rpm and there's no fluctuation of the core speeds
find in your bios Speed Smart CPU must disabled , maybe your setting still auto /enabled ... you must disabled it. if not solved , clean HSF and Fan use Alcohol, replace new thermal paste. and sure, air flow in good condition, enough intake and exhaust air ?