I hate these, "what mileage can I expect" questions.
How do you drive? Do you keep up with traffic from Stop light to s.l. or race it, or let it pass on by? Do you drive 65, 75, or 85?
Where do you drive? Congested freeways, 80 mph interstate, or 55mph rural highways?
Stock wheels and tires or plan on going bigger and more aggresive?
The best I can say is go to Fuelly and compare the 2. If you see better mileage than the Fuelly numbers on your old truck, you can probably see a similar improvement on the new truck.