mamba max very weak braking...why?

[blueb8llz]

is it the motor or esc giving my rustler weak braking?
its a mamba max w/ 6900kv motor on 2s lipos geared 55 mph on a rustler with stampede tires.
at first, i thought maybe it's because of the bigger tires, but i put my friends vilenion esc and motor on 3s into my rustler with exact same setup, and the brakes work on a dime.

i could be going pretty slow and the brakes are still weak. i have the brake at 100% and even have 10% drag brake because the braking is soooo weak.
any clues???