Since your D is an 00, I will guess that you have the 4.7 motor. While it is true that the older 5.2/5.9 series of motors were known for head cracking/gasket issues, the 4.7 motor is not.
If all you are seeing is white "smoke", and not much of it then your rig is probably fine. Water is a by product of the combustion process, and combined with our emission systems quite a bit of water is generated by each tankfull of gas you burn.
Mileage on these beasts we drive is never what I would term as good, but moving a vehicle weighing ~4800 pounds with the aerodynamics of a brick takes power.
I average 12-13 in town, and 16-18 on the hwy.
For a Gen 1, it really does not get much better than that. The different blends of gas that the EPA imposes on us can have a big effect as well.
How many miles on your D???
2004 SLT Hemi Durango AWD Flame Red
w/ 3.55 gears. Mine since 03.26.10.
2011 Hyundai Santa Fe GLS AWD V6
Mineral Gray. Hers since 8.21.14