To be honest it sounds like the diff. When it's not welded and you clutch kick it, it just spins 1 wheel for a second or so before locking they are rubbish! I ended up rolling my last z because the diff decided to open lol. If you want to keep the viscous you need to keep on a constant throttle to keep it locked, if you lift at all it just opens and straightens up the car violently. Best to leave out clutch kick entries until you get a locked diff. Just try weight transfer initiations in the meantime