[ranger danger]

Randy's gear and rpm calculator says for 4.56 gears, 31" tires and 65 mph, the RPM's would be

3 speed auto trans (1-1 Final Drive Ratio).= 3299 RPM
4 speed OD auto (.70 FDR).....................= 2249 RPM
4 speed man........................................= 3213 RPM
5 speed man. (.80 FDR).........................= 2570 RPM

Change the Gear ratio to 3.73 and you get

3 speed auto.........................................= 2698 RPM
4 speed OD auto....................................= 1839 RPM
4 speed man.........................................= 2628 RPM
5 speed man.........................................= 2102 RPM

Going from 4.56 to 3.73 is a fairly substantial reduction in RPM. Should net about 20% increase in MPG. So 9 mpg now would result in almost 2 mpg increase.