I've been driving the Challenger a lot lately and on the highway it was revving pretty high with the 3.91 gears in it. I had a 3.23 rear end from another car that I cleaned up and put new bearings and seals in so I figured I would put them in...MAN WHAT A DIFFERENCE! With the amount of torque that my 440 makes, I didn't hardly see a difference in off-the-line performance, but on the highway I can easily keep up with traffic without feeling like my motor is going to blow up! I am really enjoying driving it long distances now!