well, upgrading is definitely needed. 8 gauge wire over a 3ft span is only good for like 600watts of power or less. Take a look at this chart and it will help you
12V Wiring Sheet ,so i would expect you need atleat 4 gauge, 0 gauge would be better. But you will be doing the big 3 upgrade which is alty to battert postive, negative to ground and alty to ground. I think also it is suggested you up the fuses also but thats just what one guy who was going to rebuild my alty said to take full advantage of the upgraded alty. Right now i bet you aren't even getting half the power that alty can give. My friend had a rebuilt 120amp alt for his camaro and that was such a good alt, when he turned on his headlights and gave it some gas, the interior lights actually got brighter.