upgraded big 3 from 6-8 gauge not sure, to 4 gauge and re-inspected my amps grounds.
got some nice looking battery terminals for amp grounds and used some brass thread goo on terminals for rust protection.
also since I didn't have extra 4 gauge I just upgraded 4 channel amp ground to 4 instead of 8.
made a big difference in voltage drop cruising, and door speakers sound cleaner and louder.
sub is crushing