Unless you're towing 8000lbs over mountains the diff's not going to matter. The transmission is fully capable of setting engine rpm.Seems like a big difference between the 2 axle ratios! A hemi with 3.21s can only tow a few hundred pounds more than an ED with 3.55s!
I didn't realize how much different the ratings were ! I guess with the 3.92s u will probably sacrifice a few mpgs wether it's a hemi or an ED.
Correct me if I'm wrong !