When I had the rear end rebuilt in my ‘97 Safari, the guy installed a posi gear set, which virtually insures that my 4.3L engine and 3.73:1 axle will never break traction. Unless the ground is a little damp and I’m headed uphill. Then, when it breaks loose and starts to spin, the rear wheels start hopping up and down. There are brand new KYB Gas-Adjust shocks, an aftermarket sway bar, and an extra leaf. My question is, what causes the wheel hop and what sort of hardware would eliminate it? (That’s not my van...)