Well if it's a 4x4 then the tranny/transfer combo is one heavy mutha and since the transfer case weight is off to the side, it is also awkward to handle. With that being said, if you don't have a tall enough jack do it on the floor. If you do it with the truck in the air and something bad happens at that height and that tranny isn't secure on a jack, not only would it become dangerous, but it wouldn't do the concrete floor or the tranny any good. Of course I have always done mine by myself with a floor jack with a tranny adapter on it and it can be a pain. An extra set of hands will help. Good luck.