it depends on how much you lift the truck. if you put a really big lift you will either need to rotate the diff or get a longer driveshaft.
i am not sure an exact lift height that requires driveshaft or diff changes, but i imagine it would be somewhere in the 6 inch range. also, if you lifted it that high you might want to keep an eye on you u-joint angles.
Do not, ever, rotate the differential. Cardan shafts are meant to have the input and output shafts parallel (in this case, horizontal). If they are not parallel, you end up with a vibration, because the rotational speed isn't transfered uniformly. :disappoin There's some complex geometry behind it, but trust me.
You might be able to get by with rotating the differential, but you'll be putting a lot of stress on the driveline components that they were never designed for.
If you need a longer drive shaft, get a longer drive shaft. It's the right way.
Those who rotate the differential may not notice it, because the wide sidewall of the tires takes up a lot of the torsional vibration induced, but the universal joints, differential, and transmission still end up seeing this torsional vibration, and it will take it's toll on these parts Sometimes quicker, sometimes slower, depending on how much stress you put on these components to begin with.