Feigao 10L/Warrior 7018 cutting out

I'm brand new to brushless. My son and I just finished converting an Ofna Hyper 7 to brushless. Here is the current setup:

Motor: Feigao 540 10L (61 amp)
ESC: Warrior 7018 (71 amp continous)
Batteries: 2 x 6 cell GP3700 matched zapped packs
Spur gear: stock
Pinion: 16 tooth Mod1

We basically copied this setup except for the ESC:
http://www.rcuniverse.com/magazine/a...article_id=467

Anyways, we just starting testing it today and what we are experiencing is cutting out. It will do a full speed run and then the next run, it will cut in and out or not run at all for a few seconds and then go or it will start to go and then cut out and then start and cut out and then run fine.

Are we experiencing thermalling? It is about 100 here today. The body still has all the holes cut out for the nitro motor so it should be getting a lot of ventilation. The motor and esc are rather warm, but not having used BL before, I'm not sure if this is normal heat.

We then, almost immediately, ran it up on the workbench inside (on a carstand with the tires off the ground) and experienced none of the problems.

I thought I did my research on the ESC but did I maybe choose the wrong one?

Ideas? Thanks.

Chris