sudden brake?

[suicideneil]

Hmm, could be a thermal issue with the esc, or some kind of lvc issue in that case. Hard to say, but if there was a specific reason it would become apparent (such as thermalling). Given the motor & esc temps it sounds like you are a fraction undergeared- maybe go up a tooth on the pinion (or down on the spur) and see if the temp difference makes any difference. Does this happen often, or just once in a while with other vehicles present?...

EDIT: What are your brake settings- could be that drag brake is kicking in if you ease up on the throttle just a tiny amount without realising it....