I've been doing some research on this rear axle. The DRW trucks offer two differentials ring gear and pinion sets; they are 3.73 and 4.10. There are also two different rear axles, the AAM 11.5" and the AAM 11.8". The 11.8" is mounted in the same housing as the 11.5", so it looks the same externally, except for the cover. But the 11.8 axle has the larger ring gear and larger 300 mm axle shafts. To get the 11.8/300MM differential you need to order the AISIN automatic transmission with the 385HP/850LB-Ft of torque; otherwise if you buy the 68RFE or manual you get the 11.5” differential. Only the 11.8" ring gear and 300 mm axle comes with the aluminum finned differential cover.