[fiveohpatrol]

is the leak coming from the front or rear of the diff?

if the rear, then its just as simple as removing the cover, cleaning it and putting it back on with some black RTV (seals better than a gasket).

If its coming from the front, its probably the pinion seal.

If you want better acceleration, then go for some 3.73's or 4.10 gears. This way, when you have them installed, the leak can be fixed at the same time.