Frontier Differential Ratios ??2000/2004

The 2000 Frontier King Cab 5 speed std. tachs at around 3500 rpm at 70 mph on 15" wheels, and the 2004 Frontier 5 speed std. Crew Cab tachs at around 3000 rpm at 70 mph on 16" wheels. As a result gas mileage appears better on the later vehicle, perhaps due to overall tire circumference. Do Any of you have a reference available as to the final drive ratio for either the 2000 or the 2004 trucks, any web sites suggested for a quick reference. Is there a speedo/odometer gear change necessary when changing from 15" to 16" wheels ? Many Thanks