These numbers are just for example, but I think demonstrate the problem:

If you have a 32" tire and a 4.10 gear (3.0i), at engine speed 3000 RPM, The wheel is trying to make the car go 69.58 MPH, assuming transmission gear is 1.0 (again, just for example..removes variables). For a diff gear of 3.95 and all else the same, speed is 72.303 MPH.

So I would think that, as there are speed sensors in every wheel, they would get confused and probably create DSC and ABS faults. Turning and cornering might be odd as well, if it did not break something mechanically.

I swapped a rear 3.0i auto diff into my 3.0i manual. I hear the front is harder. Look for threads about this; there have been a few lately.

You could put both diffs in (since you have a whole parts car), but you will zoom through the transmission gears and lower your top speed, plus burn a lot of gas. Your highway cruise RPM will be higher at normal vehicle speeds.

But if you wanted to put really big all terrains on it and change the overall diameter of your tires by a good deal to match the 4.10s and your transmission gears, that would be awesome.

__________________
2001 E53 3.0 5pd