Help my JBL's keeps dimming everything on my Pontiac !!!!!!!?

my setup is 6 8'' 600 watt JBL pro speakers and 2 2K watt JBL Pro 15'' with 4 2k watt JBL Pro amps on my car Pontiac GTO with a 5 month old altinator that pushes i think 280 amps and i got 2 duralast gold 1000CCA battiries and 4 1 farad caps on '00' gauge wire and i cant find the problem for the life of me every time it goes past 48% on my favorite song 'shoulder lean by young dro?' things start dimming at 60% my battery discharge light comes on and my 'alt' gauge keeps jumping around ive gotn my altenator and amp tested and tripple checked the wiring but i still cannot find the problem