All the information you need is here, it is all in the numbers you choose, for diff locking it seems like you will need the 60K:

http://www.davesmotors.com/s.nl/c.88...t.A/id.5141/.f

3K - Best for everyday driving and offers a little better overall traction over the stock fluid. Its also less prone to leaking.
10K - Best used when your running on slippery surfaces such as grass or on loose dirt and gravel.
30K - Ideal for your sand rig offering great traction and a minimal amount of steering loss.
60K - As close as you will need to get for locking your diff without all the wear and tear on your drive train and broken parts that are associated with a solid diff locker.