Thats a video of how it is running at the moment, seems to work at the start of the video then it starts with the stopping and starting I was talking about. The second section of the video is when I turned the receiver off and it didn't seem to failsafe, it just continued to drive and when I tried to show the receiver on camera it accelerated forwards. Very strange indeed......
Odd ..yes.

However the last part ...transmitter OFF rather than reciever? ...indicates that it's probably NOT current limiting as it happily accelerates to flat out with no motor hunting.

Questions
Did you bind the BR6000 at the drive OFF failsafe position?
How have you got the XXL Jumpers set...are you using a voltage above 16v .. and if you are have you clipped the HV jumper wire?

Things to fiddle/play with.

Disconnect 2 drive motors ...one each side....see if it helps by reducing the load.
Try with a reciever battery ..remembering to clip the BEC jumper wire.

I have recently had an issue with the Spektrum recievers output signal being unable to drive a homebrew R/C steering servo ... the hunting was some what similar to your XXL symptoms.... this was solved by buying a signal line booster. http://www.spektrumrc.com/Products/Defa ... odID=SPMCP

EDIT I see from further up this thread that your running 19.2 v...you might be getting voltage sag after running for a few seconds and thus dropping under the 16v jumper limit. I remember reading that there is asolution to this ..but can't for the life of me think what it was.