What is causing my speed controller to burn out!?

i have a traxxas slash 4x4. i am using venom lipo batteries 5400mah 11.1v. this vehicle is supposed to be able to use that battery just fine. this battery i am breaking in. ( less than 7c draw first 10 charges) the esc burnt up in 2 places the first time. well it vented in 2 places. i had it for about a month and a half when the first one burnt up. traxxas was kind enough to send me a new one even tho i was way past my warranty (30 days, i bought this car on black friday). so i got the new esc today! yay i set it up for my controller. i go play in some dirt (its made for dirt and other stuff too) 10 minutes maybe 15 and it burns up again!!! everything is stock! except for: extended battery holder, and the rear A-arms. those don't make a difference. hobby shop is confused as well. any ideas??