In the past I have always gone back in forth between SG GPS and Classic Mode...personally I have always found more consistent skiing, and better results with the classic mode. I was hoping the Z box would have better control with larger serious skiers but that's not the case. So yes, I have never had great control with SG (with skiers over 185 lbs) and I have done several software updates, and tried alot of adjustments including reversing the rpm signal. PP's customer service has been great to-date.
With the zbox, like all PP control systems, the driver still has to drive the boat into the course, the driver has to be smooth, and just feather the system into engagement...if the boat comes in hot, the system will try to slow the boat down, just as the skier pulls through the gates...then the boat will try to speed up at the wrong time (as the skier approaches ball 1).... and the system is out of sync with the skier the entire pass. I think this is the one of the problems that we are having. Normally the smoothest drivers are the better skiers, and its hard to figure out whats happening in the boat when you are at the end of the rope.