Ram 2500 4x4 with Diesel engine
 

We plan to purchase this vehicle to tow our travel trailer. Can someone please comment on the fuel consumption figures, MPG, measured for this 4x4 vehicle when it is not towing, MPG highway vs. city?

Miles per gallon varies from driver to driver, road conditions, wind directions, traffic situation, etc.

Totally agree with the comment above. There are just too many factors at play.
I would love to help, but it's difficult without knowing the year. Anyway, here is what I found on Hotcars.com about Ram 2500 Cummins estimated rating of 12 city/18 highway/15 combined mpg on four-wheel drive mode.
Most charts with specs will require year/make/model/trim level to get you the estimated numbers. Check this Ram chart and how many combinations there are just to look up the towing capacity