You are not alone, far from it. USB3 seems to be very unforgiving regarding power requirements, much more so than USB2. It's a bi-directional interface now (usb2 was one-way communication) so it has tighter tolerances regarding timing and signaling (handshaking). I too have tried many cables / repeaters etc but nothing is better than the included 3' cable for trouble free shooting.
A bit of potential good news, as of this week (May 12) Nikon released firmware upgrades for many of their cameras, including the D800/e. I've installed it and have been using it tethered with longer cables, seems ok but will test more. The micro USB connector that plugs into the camera needs to be a snug fit and not wobble at all, I had to slightly file away one of the sides of the cable's plastic connector so that it would fit flush. This cable is a 90 degree angle USB3 'pigtail' cable (RR-ASMR-10GR) from www.usbfirewire.com
which plugs into a 15ft 'active' extension cable (purchased from Amazon - search for B00DMFB5OK ). This combination is the only way I found to tether and co-exist with my RRS L bracket and secure the cable into the camera's usb port. Securing is done by sliding the bracket right until it forces the cable against the camera's body. Otherwise, you can use this expensive option;http://www.lockcircle.com/lockport_d800dual/buy/index.php
They are not cheap but could work for you.
I'll do a follow-up regarding my results.
I have been having issues with both of my Nikon D800E's when it comes to tethering with cables longer then the wonderful 3' cable that comes with the camera. To be fair it doesn't only happen when tethered to C1 Pro 7 but also Nikon Camera Control Pro 7. These are top of the line of cables purchased from Tethered Tools
. This is quite frustrating especially when I'm shooting commercially with clients present.