i think its just your amp now.
if your car is fully working perfectly and your amp is shutting on and off, it must be your amp.
check the voltage at the battery and then the amp. and make sure everything is getting a minimum of 12 volts. if everything is at 12. volts + then its probably your amp.
check the fuses on your amp too. i know mine would shut on and off a while ago. then it suddenly just shut off and i was tripping off it, checked the fuses on the amp and they were blown.
check your voltage on batt and amps, then check fuses on amp.
is your cars electrical running smooth?