Dave, since you got back to me I figured I would take a look at your dilema. My buddie has a Donzi 30 ZF with the same problems. Donzi told him it was a combination of his drive height and the stepped hull. Although he has twin 250 o/b's it is probally the same problem. He gets air under the hull and it is conjunction with the bow rises which creates a low pressure region just as the boat passes. The lower pressure region allows the prop to cavitate easier. He minimizes the blowout by using his k-planes and is then pretty much able to hammer it and go, as the boat comes up bring the tabs up and then you can blow past my slow Baja!!!!! Thank god for throttle mounted controls.
25 Outlaw 502