electrical issues...havent seen this particular problem addressed

I did the 130 amp alternator swap and new big ass interstate deep cycle battery and my lights still blink when my bass hits and even under normal driving conditions. I'm getting 12.5v with the motor off and 14.8 with it on like I'm supposed too but something seems to be dragging. If I don't drive it for a day or two I get a weak start. I'm only pushing 1 12 inch sub 400 watts RMS. It also seems like its missing a but even though I'm running a beefier coil and iridium plugs. If anyone could tell me where I should look that would be great. Replaced virtually every fuse in the truck and cleaned the relays so I'm pretty much stumped. Any and all help is appreciated. Lights also dim with the sub turned off just not as bad.

did you upgrade the wires from the alt to the batter and the ground wires? use 0 gauge wire in place of all of those and you will be good.

Ok while you upgraded some things.I see you did not mention replacing your battery cables?Those old oem ones if your still using those might explain the dimming.I upgraded my cables two yrs ago pos/neg and they MAKE a big difference.Just update if this has or has not been upgraded.More power requires better grade gauge cables,plus shear old age reduces a cable to handle power and conduct properly.

I up sized the charging wire and battery ground to 4awg OFC kicker brand wire. Didn't mess with the positive lead from the battery. I tried running more 4awg ground to the motor from the battery but it tripped the oil light on so I took it off. Been contemplating a big three kit for a while but not sure how the positive lead ties into everything as its still factory wrapped.