Aftermarket radio problems

[rzarock]

I've installed a post AM/FM radio from custom auto sound on my 72 C20. Everything sounded fine until I installed a small subwoofer and 150W amp to round out the sound. The sub cuts in and out at idle but sounds great at highway speeds, or when engine is not running. I've installed a new 55 amp alternator (stock was 42 amps), a new external voltage regulator, changed battery cables, upgraded all grounds, upgraded power wire from alternator to battery and the problem still remains. At this point I'm thinking there just isn't enough current to power the new radio and amp. I'm thinking of upgrading to a CS-130 alternator but before I do I was hoping someone could point out something I missed that may solve the problem. Also, has anyone ever used the conversion kit from american auto wire. If so were you satisfied? It seems pretty simple.

http://www.americanautowire.com/prod...rsion_Kits.cfm

Thanks.