Basically, your motor is also your brakes. Upgrade the motor with stronger magnets, and it will stop quicker, I think. Correct me if I'm wrong somebody, but when I upgraded my 1/10 Rustler with a competition stocker it not only went faster, it stopped quicker.
The brakes work like Dynamic brakes on Trains. The motor will generate power when coasting but braking trys to force it through some very strong resistors to slow it down by not letting it make electric of any sort!