9L/9920 Just Stops

[brijar]

I was just out driving my 9L/9920 E-Maxx geared 16/66 with 2 speeds on REVO 3.3 tires running 13 RS GP3300's and one RS Green 3300 cell all soldered SxS with Deans all around and the 3.5mm gold plugs on the motor.
I have a small berm (man made hill) in my backyard that is about 3 feet high, and fairly steep on one side, steep enough to catch some air. I was jumping this, and after about the 4th jump, when I turned around after landing perfectly, the truck just stopped. I went over to it, and gave it some gas, but it didn't move. A beeping noise came from somewhere, maybe the ESC or the motor. I tried it again, pumping the throttle, but the motor/ESC just beeped more and the 9L made, maybe half a turn, very weakly. It is very cold out when I was driving, about 10F. I have 2 small fans (40mm .08 amps each) on both the motor and the ESC to help keep temps down when it's hot. It has done this before when I jump, but it would usually recover after a minute of sitting.
I'd like to know what's causing this, as it is very annoying. I have a steel idler gear in 1st gear (they were out of the "pairs" when I ordered), but I don't think I re-lubed it when I took the tranny apart a couple days ago. I'm running a 6v receiver pack that I had just recently charged. The steering and shifting always work just fine, only the throttle has issues.
Could it be too cold for the ESC? Maybe it doesn't like my batteries, but it always works just fine when I do speed runs for the whole run.

Could anyone help me out here?

Thanks,
Brijar!!!