Okay I need to verify something here. The specs show the Hellcat A8 comes with 2.62 gears and the M6 comes with 3.7s. When I build my Challenger Hellcat on Dodge.com it shows my M6 with 2.62s. So what gears actually come with the M6?
Using a lower rear end gear in a boosted car is normal.
In a NA car like the 392 your using the mechanical advantage of using a steep gear ratio like a 3.92 to get up and go.
But for a boosted application like the Hellcat you don't need to use the rear gear as much. Your mechanical advantage now is the blower. With a lower rear end gear you keeping the car in boost longer.