89 f350, should front and rear gear ratio be the same?

 

Absolutely yes

 

Yep, sometimes it will be like (example) 4:10 rear/4.09 front... Don't ask me why, I don't have a clue why.... But I have seen it over and over through the years..

 

The reason they are sometimes off by a few hundredth is due to different numbers of teeth on ring and pinion gears from front to rear.

Example:
Front diff has 41 ring gear teeth, and 10 pinion gear teeth, 41/10 = 4.10 ratio
Rear diff has 37 ring gear teeth, and 9 pinion gear teeth, 37/9 = 4.11 ratio

This will work on the same rig front and back, but any more than a few hundredths difference front to rear will cause bind if you put it in 4x4 with any kind of traction

 

The slight difference in ratios is because the front wheels take a longer path around turns. Some makers think it's a big deal, some don't...