1990 t bird current issues?

So I'll give you my run down on what I got and my issue.

New 75 amp. Alt.
Bluetop Ultima Battery 3 months old
4 gauge Power wire running back to the amps connected first to a Rockford Fosgate 10 Farad Digital cap.
Power BD1000 Rockford Fosgate amp. running 2-10" T1 subs in a sealed box.
Phoenix Gold 4 ch. Tantrum 400.4 Diamond Audio Comp. D6 6-1/2" front and rears.

My Issue is I cant keep a constant amprage draw for my amplifier.  It runs flawless for about 1-2 mins. and then its starved for power and the bass is much less with excessive headlight dimming.  I have heard that the wiring in the older cars could be the issue, but not aware of how to start to fix it.

So my only thoughts are I either need to fix the wiring or buy a bigger Alternator.  I have never had a problem like this before owning a similar system in a Honda Civic which had a less ampreage Alt. and a much smaller Cap. Any thoughts or suggestions would be much appreciated!  Thanks

Corey

understand also that your blue top optima is a deep cycle battery.... not an ideal application.

loose the cap too..

Why would I loose the cap?  Just wondering?  I always thought a cap helped... But I will go thru and do the big three and look into upgrading my 4 gauge to either 2 or 0/1 gauge.  And the battery, I didnt think it was as big of a deal as it is.. I'll look for a red or yellow top and stick that batt. in my other vehicle that doesnt have a system in it.. Thanks for the info!!

Corey