Video will at least be interesting to serve as a starting point reference to compare future progress against. You may also find the root cause of your Z turns. Hint - start at the beginning of the turn and find which body part(s) move first. Although you already know what "your problem" is, since multiple examiners, et. al. have been unable to fix it, video MAY give you your breakthrough. Not likely, but worth the try anyway. If you do get yourself taped, consider posting a copy here for the vultures to pick over.
One interesting approach to teaching is that you can not teach by simply taking something (e.g. excess rotation) away. You need to replace it with something else. Do you know what you need to replace your rotation with?
Check out this thread about Z turning
. There's good stuff in there.
From what you've described, it sounds like you need to "own" the movements on the groomers before trying to get them working in bumps and steeps. The good news is there are tons of exercises that can help. The bad news is that there are tons of exercises that can help. The really bad news is that you either have to pick through the list for yourself, or pick a coach to pick for you. The trick is finding time to do this stuff to dial it in. 5 day clinics like National Academy or Pro Jam can do wonders. Since you're in Mass., dedicating a weeknight for doing drills is another alternative. Don't overlook the opportunity for teaching to help your own skiing too. When doing wedge and christy demos, focus on the slight movement of the center of mass and rounding out the tops of your turns.
With regards to drills, here are 3 of my favorites for what you've described:
1) Bamboo turns - ditch the poles & carry bamboo across your shoulders; keep the boo level to the slope pitch at all times.
2) Ten toes (aka take some vertical with that turn) - focus on getting all ten toes pointed in the fall line during your turn; kill extra speed by finishing turns going uphill.
3) Snowblades - EXTREME
edge angles please. If your tips wobble, go on a higher edge. Go fast. Dig trenches (i.e pure carves). Rip your turns so that you scare the tourists.
If you want more exercises (although you're likely to get way too many just from this thread), you can check out some of my clinic notes from the 2003 National Academy
and the 2004 Snow Pro J
am. Here's my main clinic note page