4.56 yukon in rear factory still in the front but I dont plan on using the 4x4 i went from 35/14.50/16 to 33/12.50/16.5 got a lot peppier after i put the smaller tires on. And the truck has 248k on the body the tranny before had the same mileage and he ran this thing in the mud every weekend I suspect that had something to do with it.