help with cogging

I need some help and I am dying to get the E-Maxx running! 12020, 8XL, UBEC, 12 cell IB 3800, deans connectors, stock receiver.

Being new to this, I am assuming what's going on is cogging. When i give it throttle, it will hesitate/stutter and then take off.

Thus far I have:
1 - upgraded to IB 3800 from el cheap O's
2 - moved the reciever to the back
3 - UBEC in front, to the back
4 - unplugged the UBEC (kept wired to battery) and plugged in a reciever pack

What else can i do??

Thank you!