Is it the 3.8 or V8? If it's the 4.6L you never got 320mpg in the city actually 170 in stop-n-go traffic is a little low but if you have your a/c or heater on those numbers are prob right. If its the V6 well.......never owned one or worked on one so im no help to you there.
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Rest In Peace Hypsi87, you'll be missed.