Look real closely at the rear shackle angles as already suggested. If yours are in the stock location you need to move the upper pivot point forwars to the front of the car so you have a 30 degree or more angle on the rar shackles when sitting still with the weight on the rear tires The rear shackles need to be able to move forward under acceleration to help lift the back of the car up so it pushes the rear tires into the ground If there almost straight up and own when sitting still they will swing forward past the staright up and down and start pulling the rear spring eye down