I could be wrong here.......God knows it's been a while since I've set up a rear suspension in a Mopar race car, but the way I remember it is, you don't choose the spring based on the vehicle's weight.........in other words, say your car weighs 3800 pounds, I don't "think" that's how you choose the spring. I believe you chose based on spring rate, not the weight. I believe you may have too much spring under that car.
Now, I could be so far off base I'm a lunatic......wait, I am a lunatic, but I could be slap wrong. But something sticks out in my mind about that. I can tell you this. I know someone with an almost 4K pound 73 Charger in north Georgia running 9s. He has the 002 and 003 SS springs in his car and it LEAVES FROM HERE. lol