So, if you were switching gears from a 3.73 in an Excursion with the V-10, would you go right to 4.56 or 4.30? Gas mileage is not a concern, and it's in a 2WD.
$1,000 ballpark parts and labor. I have and highly recommend Eaton TrueTrac differential. It is the only differential that both differentiates and transfers torque at the same time. Will add about $600 to the cost.
4.30 or 4.56 is about 5%. I would probably go 4.30 but 4.56 if dedicated to towing. Fine either way, even 4.88 could be considered.