rear tires unloading
Not only was the factory length rear shock not long enough, but I also added AFCO Double Adjustables. Even on maximum extension dampening, it was not enough to slow down the separation. I contacted AFCO and had the shocks re-valved using their "Big Dog" valving, which allowed me to dial in the body separation and eliminate the issue successfully. My traction is the best it has ever been.
When my '70 manual trans E-Body would launch, even on the street, the rears would jump off the pavement like you describe from the hit from hard launch. It's a leaf spring suspension with a properly adjusted slapper bar to control the front-segment's spring wrap.
Not only was the factory length rear shock not long enough, but I also added AFCO Double Adjustables. Even on maximum extension dampening, it was not enough to slow down the separation. I contacted AFCO and had the shocks re-valved using their "Big Dog" valving, which allowed me to dial in the body separation and eliminate the issue successfully. My traction is the best it has ever been.