It might be worth your while to have somone who is up on them to go through it. The clutches may be worn or load not set up right. Like my freind said they are twitchy if set up wrong and you may be getting to much lock up at the wrong times. The high torque cars are sensitive to how abrupt the diff locks under loads (ie comming out of corners). Since the Z's are tail twitchy this could be a problem.