I think it's the tranny. My F150 does the same thing. I believe the Crown Vic has the same tranny, 4R70W or AODE. It has an open cooler line with no thermostat like the 4R100 used in the Lightning and some of the F-150's, 250's, etc... I'd let it warm up for a good two minutes before taking off. If I let mine warm up completely, it goes away.
John
John