Wheelhop in an A-body is caused by the design of the rear suspension. In its stock form, the upper control arms are generally tilted at an upward angle from the rearend housing. As power is applied the housing tries to rotate in the opposite direction of the ring gear, that is, the housing is pulling on the upper control arms. But the body has much more mass than the rear, so instead of the body being pulled down, the rear actually pulls itself up, unloading the rear tires. The tires then lose traction, the housing stops pulling itself up which gives the tires a chance to grip and the whole process starts all over again. When this happens a dozen times a second, you got wheelhop.