rcracer37;

You'll find that the truck will handle better with some grease in the diffs. Since the diffs are not sealed, oil will just leak out into the housings.

I personally like Silicone Grease for unsealed diffs. It does not seap out like regular grease and lasts many months between rebuilds.

As a second choice, a good High Temp automotive grease (GL5 spec) should suffice.