The differential is going to be a limited slip Getrag unit that I pulled from a 2010 Challenger SRT8 I parted out. The Challengers with the 6 speed manual transmission received a 3.91 ratio vs the 3.06 that came with the automatic. My 2010 Challenger daily driver has the exact same 6.1L, 6 speed, and Getrag 3.91. With the .50 overdrive ratio, I am turning 2,000 RPM at 85mph. Should be fun off the line and still comfortable on the highway. The differential just got installed so that exhaust could be routed.