The Jeep Grand Cherokee with the 3.0L V6 Diesel MPG is projected at 20 city and 28 highway for the 4x4 model. I would expect the Ram to come in around 18 city and 26 highway, hopefully. With 220ish HP and 420ish ft-lbs. of torque, that's pretty sweet.
The downside is that for the GC, it's a $4,500 option. If it's the same for Ram, comparing the fuel mileage savings to the Hemi (14/20), it would take approximately 7.5 years to make up the difference (15,000 miles a year, fuel @ $3.50 a gallon, highway mileage used).
It's kind of like the Volt. Awesome concept, but the cost isn't there yet. Hopefully if the 3.0L makes it into other platforms, (Wrangler is a likely target) the cost will go down.
As far as the transmissions, we're using the same suppliers as other OEMs out there. ZF, Aisin, etc.