To all the folks that has issue with fluctuating blacks or flicker in 3D mode, did you block the power led light? I also had the same issue, and had the LED light blocked. I decided to remove it temporarily and to my surprise the issue has ceased, I tested it with Underworld: Awakening, since that movie exhibit the issue the most.
So, you guys can try that remedy and let me know if it fixes the issue.
Television: Panasonic TC-P65VT60
Receiver: Yamaha RX-A2010
Speakers: Energy RC-70's, RC-LCR, RC-10 (4), JTR Captivator 1400, Rythmik FV15HP (2) and Velodyne VDR-12 (3)