Those numbers are ratios of driveshaft RPM to Axel RPM. With 3.73's, the driveshaft turns 3.73 times for every one turn of the axels. So, the 4.10's are a little "lower" ratio so the engine RPM's will be a little higher at a given speed than with 3.73's. 4.10's will give a little quicker acceleration, 3.73's will give a little better gas mileage, a little less noise. Make sense?