383 build for efficiency

I'm with 273 on this. Why would the rpm at which peak torque occurs, which is measured at wide open throttle , correlate with part throttle fuel efficiency? I believe it's just an old myth. A new Challenger 6.4 Hemi makes peak torque around 4200 rpm. Shift it out of overdrive into one of the lower gears so that you can drive at 4200 rpm at 70 mph and see what happens to your mpg.