Fuel mileage 1500 vs 2500?

I am going to be buying a used 1500 or 2500 in the next week or so and I can't seem to find much info on mpg. I know the 1500 gets around 16-17 (5.3 Z71 4x4) in a 50-50 mix of country roads and towns because I rented one and put 800 miles on it, but what does the 2500 get? FYI- I'm looking at 2001-2005 4x4's, would love a manual but all I can find is autos. Any numers on mileage would be appriciated. Thanks

It will be a lot worse. 2500's aren't EPA rated but you'll see 13 max in combined driving.

my 2001 1500 ext cab 4X4 5.3L got 15mpg around town and 18.5 highway, my 2002 2500hd crew cab 6.0L gets 11mpg around town and 15.5 highway...on the plus side i hauled a 10,000 lbs flatbed trailer from chicago to dallas and got 10mpg going about 80-85mph the whole way there