2WD Verses 4WD--gas mileage?

[Montana_89]

I realize that the topic of "2WD verses 4WD" has occurred any times so I apologize for any repetition. Living in New Jersey, I am wrestling with 2WD or 4WD on buying a 3500 dually-8.1 engine. I haven't read much about the mileage difference between the two--towing or solo. Could anyone help me? Thanks!

Art & Roe
2003 3670RL 5er
Mt. Laurel, NJ