Edmunds.com recently completed 12 months driving a 2012 Grand Cherokee SRT8. They experienced no major problems, and enjoyed the 465 lb ft of torque that the 6.4L Hemi V8 provided. Fuel economy averaged 14 mpg.
http://www.edmunds.com/jeep/grand-cherokee/2012/long-term-road-test/wrap-up.html
The 2014 Grand Cherokee with 3.0L diesel with 8 speed transmission makes about 10% less torque than the SRT8. I bet the diesel gets almost double the fuel economy, and still provides smoky burnouts when requested.
http://www.edmunds.com/jeep/grand-cherokee/2012/long-term-road-test/wrap-up.html
The 2014 Grand Cherokee with 3.0L diesel with 8 speed transmission makes about 10% less torque than the SRT8. I bet the diesel gets almost double the fuel economy, and still provides smoky burnouts when requested.