Need advice on what my next step is

[Audio noob]

So I have a Cadillac cts I recently just purchased  2 15 competition subs kickers and a 3000 watt hiifonics brute grade d mono block amp now my issue is they will be at full power banging at least in my opinion anyway I get to my destination turn car off when I turn on the car again(sometimes it's 2 destination )) the quality of the bass goes down drastically maybe a quarter of it's capacity  also the wiring for the install was in the car at time of purchase I'd say installed in 2010 maybe 2012 I can post pictures of set up tomorrow morning any ideas or advice greatly appreciated thanks

[Dafaseles]

Have you ever checked the voltage at the amp during the diminished sound? My guess is you need a little more electrical. Maybe just a second battery

[Audio noob]

I have not will do tomorrow thanks for the reply appreciate it