Funny thing is, I recently traded 3.73'2 in both my Ranger and Lightning for 4.10's and would never look back. And also, on both, the speedometer reading didn't change a bit. Reason, on both, the speedometer reads off a tone ring in the rear axle that counts teeth on the ring gear. And that tooth part bolts onto the ring gear. Therefore, the tooth count doesn't change and the speedometer stays the same. All the main streets in my area are almost exactly one mile apart. I still get exactly one mile change from one street to the next, didn't change one whit. Look for a sensor wire on top of the pumpkin. That is the speedometer sensor.
Maybe the 8.8 is different? And a four cylinder with an 8.8 while my 3.0 V-6 has a 7.5? Someone must've changed it.