Well, after nearly two months, I'm almost got this thing figured out. There were many, many things wrong.
1. I did the big 3 incorrectly. Because of spotty information I did the big 3 with power, battery ground to engine, and engine ground to chassis ground. I did this in part because of using a Steve Meade vid for advice on it where he did the same. I re did it with alt to battery, battery chassis ground, battery engine ground, and engine to chassis ground, making it a big 4. I recommend doing this if you are doing a big 3, pretty easy to add a extra ground
2. My crimping was terrible. I wasn't using a proper cable cutter to cut my 1/0. Because of this the wire would not completely go in the ring terminals like it was supposed to. I bought a wire crimper and re-did terminals as needed throughout the whole truck.
3. My battery terminals were not properly tightened. Pretty self explanatory, I had been disconnecting/connecting so much that I just assumed they were good but they weren't.
4. Use of a distribution block. I switched to making my run of 1/0 to go straight to my sub amp and ran a separate wire to my speaker amp. Seemed to help with volt drop and cleaned up sound.
5. My battery is bad. I have a Northstar 34/78 coming this week
6. When I did my first install of my Mechman alternator, I used a incorrect sized terminal (the Mechman was a 5/16 bolt and I was using 3/8 lugs)
7. Probably not related but I ran out of heat shrink and used electrical tape. DONT DO THIS.
I'm still having a little bit of a voltage problem but I'm 90% sure it's attributed to my bad battery. I'll update this thread when I install it to report the difference and if it fixes my issues for good. What I know for sure is the changes above that I fixed have made a world of difference. Much less drop and holds higher. Much cleaner sound as well. I hope someone reads this and learns from my mistakes so they don't have to go on the wild goose chase I've been going on trying to fix this thing. Also, if your'e having these issues and you think you have good grounds, chances are you don't, trust me lol. I swore up and down my were good, went off everything I learned from youtube etc. but they were bad. Sorry to everyone that told me to check my grounds.