STRANGE PROBLEM Emaxx BUILD

I 'm just finishing up install of a feiago 7xl motor, MM esc, castle Bec, running 2 maxamp 7 cell paks. when i pull the accelerator Fast and release it, the truck will accelerate on its own for about 1 to 2 secs. Im using the futaba 2.4 gig fast system. It does in for. or rev. If you accelerated slow it works ok. the esc settings are
punch 4
start power high
motor timing normal
motor type brushless
Any suggestions would be appreciated