Once in a while the car will start but the gas peddle doesn't rev the engine and putting it in gear does nothing

Once in a while the car will start but the gas peddle doesn't rev the engine and putting it in gear does nothing. The transmission handle will be in the "D" or drive position but does not engage but just sits there. About a month ago AAA changed the battery for free and that seemed to solve the problem but then it happened again. But this time when I turned the key off and restarted the engine everything worked fine again. I am concerned about this happening at an inopportune moment and getting stuck out in nowhere. Any assistance greatly appreciated.