Nemo667 - thanks for the info about the issue Don had, just the type of info I was looking to get. The issue wasn't the hemi but the softer springs in the power wagon which is designed for off road. The power issue was mainly because of the elevation, but also partly because of the tires. The 4.56 gearing didn't compensate for the 35" tires.
RamTC - I've seen reports from a number of folks who when running 60-65 mph get 16.5 - 17 mpg (calculated) highway empty, but these are with 3.73 gears. Figuring about 0.5 mpg loss with the 4.10s due to 10% higher rpm.
One thing that I haven't been able to find is the torque curve for the 6.4. It is hard to believe since the engine has been available for several months now. Only thing I've seen is that the engine makes 90% of torque by 1200 RPM.