2 alpine type r's and 1.1000 pdx problem

ok first the details. 2008 toyota scion, have two alpine type r's that are 2ohm and the alpine 1.1000pdx. the way i have the speakers wired is like this, each sub is wired in series 4ohm load. then the two subs are wired parallel 2ohm load. have checked with meter and shows 2ohms. i have checked on line and seems to be wired right but anyone chime in please if this sounds wrong. so here is the problem, the first month and half subs ran and hit hard. then out of the blue they would hit and kick the amp to protection. cant seem to play the system anything over 25 on the head unit. all this is new, nothing used. i have checked subs and they are fine. had amp checked and was told fine. and if system is ran hard for a long period of time and then you shut off the car, starts hard the next start. what could be the problem? will it kick if voltage drops? it has 4gauge wire ran to the amp, someone told me to up everything to 0. does that sound like it could help. maybe a cap, a better battery, or larger alternator. im not sure cause this is the first time this has ever happened to me. thanks for any help or tips someone can give me

oh and before anyone asks, the gain is set corectly.

When it fails next time, check your voltage and ground with  a digital volt meter.There is no such thing as free installation!