I'm going to go out on a limb here and say that is obtainable. Seeing how well these 3/4 tons can achieve 20 MPG in a 8000lb + truck along with a larger rotating assembly, brakes, frame, etc a lighter more efficient engine should be able to see those kind of numbers.
As always the actual mpg will depend on driving style, conditions and maintenance. The EcoDiesel is likely to best the Hemi by 6 to 8 mpg in most situations. Open highway cruising has been reported to be over 30. The EPA rating will probably be less as is often the case with diesels.