AWD to RWD chevrolet trailblazer ss mpg?

So a RWD does 15 in the city and 19 on the highway. The AWD does 14 in the city and 17 on the highway, but you can switch the car back to RWD in a AWD model, and when you do does the mpg end up like the mpg for the RWD version, or lower because it is heavier.