well it sounds like you have one that either someone has put a mechanical LSD into, or for one reason or another came with it-when I had my SRT-6 on the lift, and in PARK, you can rotate one tire clockwise, and watch the other tire go counter clockwise...my car has done this since it had 900 miles on it, so I'm sure it is not because a mechanical LSD is worn out etc...the rear end in my car is wide open and utilizes the electronics to mandate wheel spin...I also have on video autocrossing my car and you can distinctly see the inside tire spinning easily for a moment before the electronics clamp it down and allow the outside tire to take power, or the computer cuts engine power. I have discovered that it is a delicate line between going fast on the edge of traction and loosing because of the electronic nannies!