Most OEM diff gear ratio's are designed to be 'about' 10% apart
Meaning that if you have or considering a 3.73...and going to a 4.1...the drive
shaft will spin 'about' 10% more per tire rev
Going to the next lower gear will ADD another approx 10% more drive shaft rev's
per tire rev and so on...
Meaning that the ICE will spin about 10% more and that does NOT always translate
to using more fuel
Some times, it can actually use LESS fuel because it is no longer working as hard
So much depends on the rest of the factors
