I had posted this in another thread, but I think it's worth mentioning again as it appears to be the root of the problem. The part of the grip that replaces the battery inside the camera is not quite large enough to fill the space. This allows the grip to rotate a bit and flex (no matter how tightly it's screwed down), which can allow the contacts to lose contact, as well as making the whole combination feel sloppy. What worked for me was a couple of strips of business cards simply placed on the grip like so (I didn't even use tape):
http://members.cox.net/sideman7/Gripfix.jpg
It's hard to believe, but this simple fix makes the grip solid as the one on my D60, even with a 70-200 IS. My only issue at this point is that the batteries seem to drain quicker according to the camera (the chargers say the batteries are still half full...), although I don't know if it's unreasonable for the low (half) battery to show up after 600-700 frames with constant IS and Al Servo use (never used Al Servo on my D60).