What do i gain from taller differential gears??

if your staying with your 32's you can regain that fuel efficiency by getting the 4.56 gears but anything over 32-33" you should go with the 4.88's

 

Thanks for the explanation.
The only reason I mentioned it is that I've made the mistake of using the ratio calculator without considering tire flattening. I ended up

Thanks for your description.
The only reason I mentioned it is that I've made the mistake of using the ratio/RPM calculator without considering "tire flattening" and was disappointed with a ratio too low.
Also, some tires, like floatation tires, flatten more than LTD type tires, and the correction is even more pronounced.