Need wiring help - aftermarket electronics messing with transmission

Hey all, I have a 2003 Peterbilt 330 that has had some transmission issues (Allison 2000) and the shop said the issue is due to a fluctuating power supply caused by the aftermarket lights and stereo on the truck. The first go around, they replaced 2 batteries and added a 3rd which worked for a little. Now the 3 new batteries don't hold power and the trans is acting up again. I need some help trying to isolate the culprit for the constant power draw.

My main questions are where exactly does everyone tap wires into for aftermarket lights? How can I determine what is the culprit for power draw? Overall, am I seriously overloading the electrical system?

The aftermarket components consist of:
- Air cleaner light bar with x12 3/4" marker lights on each side of the truck
- x6 3/4" marker lights around the flatbed
- 36" light bar on the headache rack
- Led light strips in the 3 toolboxes
- Pedestal lights on each mirror
- Planet Audio single din 10" touch screen with 4 speakers in factory location
- x1 Scar 8" subwoofer with an 800w amp

Now I know this is all creature comforts but now I am wanting to sell the truck and don't want holes everywhere from me stripping everything. All of the aftermarket marker lights tap into the headlight switch and run off its fuse. The light bar and toolbox lights run to the battery with their own switch and an in-line fuse. I didn't wire the stereo but it all looks like correct wiring. The amp for sub goes directly to the battery with an in-line fuse (wired as instructed through manual).

The alternator in now not passing a load test so I just ordered a new one but I want figure out what is pulling power and causing the trans to go crazy (coming out of gear at every stop, have to recycle the ignition to clear code and it runs again until the next stop). At first the batteries would be dead at every cutoff but I unplugged everything aftermarket and it will start back up without a jump. The trans still does its thing but Im hoping the alternator will solve that issue.

I know this is a long read and I appreciate anyone who takes the time. I also know that this isn't a car electronics forum but I don't think those guys could understand the issues since it is heavy truck related. For what it's worth, I am 21 y/o so please give me some grace for my stupidity. I would appreciate any input/advice. Thank you all in advance.

 

Truck pics

https://imgur.com/EbcYeHe
https://imgur.com/vAxexUm
https://imgur.com/GdNScyj

 

Goodysnap - I have considered the master disconnect but that wouldn't necessarily solve the transmission issue while running. I think a mix of the power draw and weak alternator is the real issue to get it running correctly. I ran the truck yesterday and it certainly ran much better with everything unplugged but it still threw the trans code at a few stops which required me to recycle the ignition. I hooked the battery charger up to see how it does fully charged since the alternator is struggling but haven't had time to run it.

The shop I took the truck to seems to be a pretty trustworthy Allison service location. The first time it went in for the issue, they said the TSM was throwing multiple voltage codes and had to replace batteries to move forward. That resolved the voltage issue, but there was something leaking internally that got the harness wet (the actual description they told me went somewhat over my head so this is what I collected). They fixed that issue and cleaned the harness and truck operated as it should. It ran great for a few weeks then started to come out of gear at stops again. When I took it back they said the brand new batteries were dead and alternator is weak causing the same voltage codes. All due to the aftermarket accessories overloading the system. It does seem to be a voltage issue but my research led me to a bad solenoid (common issue for these) and it seems to have the exact same symptoms. The shop didn't mention anything about that but that's the only other thing I could think of.

AModel - Yes all LED. I didn't think it was excessive so I will find the weak link. I wired what I could to spare fuses and original circuits unless otherwise instructed but installation instructions (like an EGT gauge I added had a connection for headlight 12v, ignition 12v, and constant 12v for some reason). One question I have with the fuse block is, if wired directly to the battery, what would be any different than wiring individual circuits to the battery (besides cleanliness, which I am on the same boat as you). Would it need to go through the ignition or have some sort of switch between the block and battery to eliminate power draw?