54 is somewhat on the high side, though nothing dangerous. You're sure your cpu fan is running well? Also, are you sure the heat sink is attached to the cpu well? Esp. if you installed it yourself, there could be problems with the contact, which would result in poor cooling.
Another thing- where is the computer box itself? Enclosed spaces, such as in many computer desks and such, will heat up and keep the whole system running warmer than if you allow some space around it for ventilation.