Diffs! I run a IRS D ring diff. I outfitted diff with acer racing Cermanic diff balls. Built it with Niftech diff lube. I have polished rings with 1000 grid sandpaper. This is the smoothest diff I have ever built! IRS (Dave) says to scuff up rings! I differ with him about it. Because if you use a diff lube & balls that isn't up to it, you will have to do as he has. I'm not a fan of Grade 25 balls either. I have been building diffs since 1992. My XXX-S have diffs built same way as my L3. They have lasted now for 6 months & still silky smooth, when I first built them. I also outfitted L3 with cermanic bearings from acer... They are super sweet! You can go to www.acerracing.com For all your bearings & Diff balls. Their HCCA Diff balls are "grade 10" if you go that route...A little bearing info: balls are graded by for roundness. 1 thru 50. 1 being the best roundness. You really can't beat acer's prices too.