I have 70k on my 3.0 at top off the coolant about every 4-6 months. Did you happen you use the heater or defroster durring the time the level went down? If you have recently started using the heater you may have had air in the heater core. Sometime new cars have a little air trapped in the heater core and when you start to use the heater the air will escape and be replaced with coolant so you may see a small drop in coolent level at the expansion tank.