8 3/4 ring gear change for optimum low end performance

3.73 gears were not an option "back in the day" but are now.

For reference my factory 3.92:1 Dakota runs just fine on the highway but the MPG falls way off between about 50 MPH and 70 (20-23 at 50, 16-17 at 70).
I documented the RPM at speed with 255/55/17 tires elsewhere on FxBO.

I've actually been thinking about stepping down to 3.73 or 3.55 to see if I can get that MPG sweet spot to move up a bit.