Keeping the RPM in the sweet spot is the key. It looks like you're cruising along at 1,800 RPM.This is the closest I have, found that running 82 I got 4mpg better than 85 and with a 120 mile daily commute
it makes a difference.
If I'm towing at 65 mph with 3.92 gears, I'm also in the sweet spot, and pretty close to peak torque. If not towing, 3.22 gears is the way to go. If towing, the 3.92 is the way to go. The question remains, how much towing does most EcoDiesel owners actually do? Is 3.92 really worth it?
I do a lot of driving in the Rocky Mountain region, so that makes the 3.92s valuable even when unloaded (less downshifting). For me, the 3.92 is an easy decision. If I lived in the Midwest, it might be a tougher decision.