You want to be careful with your battery choices. Optima is a great line of batteries, i have 5 between 2 vehicles. The red top line is good for starting, mainly used on high draw starting applications such as dragster, bigger trucks like diesels and the like. I bought a Red Top for my mom'* truck and it works like a champ. If you are looking for a good deep cycle, especially for a sound system application, i'd go with either a Yellow Top or a Blue top. I had 4 yellow tops in my car for my system and they are great for those days you want to keep your system goin low while ur washin the car or partyin at the beach or what not. The yellow tops are good for starting as well but they are built for accessory use like systems, lighting, winces, etc. They are quite pricey but worth every penny. It'* a great idea you did the Big 3 and have a high output alternator, totally worth every penny as well. IMO i'd post that Red Top on the forum f/* and invest in a yellow top or if you want to spend some extra coin, go with a Powermaster, also a top of the line deep cycle, high draw battery. Just thought i'd add my .02 since i had the same problem. I've got 3000 watts runnin through my trunk so all the upgrades helped alot, but never fully rely on your battery.

Did you upgrade pos wire from alt to bat? & neg wire bat to chassis?
I just did that today and no more dimming. but my rear view mirror did fall off.