I have an 08 Ranger with Auto, 3.0 engine. I plan to upgrade to 16 inch wheels and taller tires since I have the 4:10 ratio and would like improve milage a bit.

What do I have to do to recalibrate the speedo?

 

Not sure if Forscan can do that, but maybe, its a software that "talks" with Ford computers

In 2001 and up Rangers the engine computer(PCM) gets the speed signal from the OSS sensor(on transmission), then converts it from 20,000ppm to the 8,000ppm signal the speedo/odo needs
Computer is programed with factory rear axle ratio and tire diameter to do that calculation, wheel size doesn't matter just overall diameter

But Ford can for sure do that, not sure what they would charge