It depends on what power you're pushing. If your running over 8 cells, you should consider an Al diff cup (comes with a steel diff gear). Much stronger than the plastic diff. And the spider gears inside are a direct swap. Only problem I found with this upgrade is it leaves you with a steel diff gear and steel top gear spinning against an Al idler. Strong, but the idler will file down in NO TIME. Mike and I have discussed producing steel idlers and including them as a package with the Al diff asm. Not sure if it's on the priority list though.

I personally run high HP, so I have a full steel geartrain in mine (yes, even the idler is hardened steel....custom made from gear stock).