Whether you're running a stock flattie and rearend or hopped-up overhead and quick change, you need to run a good gear lube. Remember that your rearend was designed fifty plus years ago and needs all the help it can get.
The biggest improvement you can give it is a lubricant that will allow the gears to survive the highway speeds that cars see today. L.E. rear end lube is what we use in our 350 mph streamliner, that uses a V-8 quick change, without failure. The "red stuff" provides superior lubrication for long gear life. You can't win if you don't finish. We suggest 90 weight for the street and 140 weight for extreme uses.