i agree with your decision completely
if possible, change to a asus, new in a closed box, open box game me only problems in the past when i bought cpus and other stuff
the cpu was present on another faulty machine?
this sounds important, also the ram, try to find one, at least for a moment to discard it
have you verified the psu, what voltages is delivering? instability could be caused by the 12v line to cpu fluctuating