I don't think simply shutting down 4 cylinders works. It requires many more computerized adjustments to engine and electronics.
The Hemi engine you're talking about had 390fp torque and 340HP and even 4 cylinders can push the car at cruising speed,
But on the other hand, Aurora has 4000 pounds weight and 250HP which is equal to a little 2800 pound car having 150HP, which is good but not great.
To save on gas I'd suggest replacing your spark-plugs with NGK Irridium sold at:
www.NGK.com
I'm getting 29mpg with them on freeway and 24-5 city.
Also empty all the weight from trunk and backseat and lose a few pounds yourself
jk
Oh, next time.........Buy a lowmile Toyota Camry or Corolla. No other car has their quality/reliablity