Hi...LOW ;)

So, I'm a newbie here. I'm a special mechanic by trade. I built Elevators so I have a understanding of how things work and common sense. Lots of stress lately as Ma got a Tundra Lemon. It's a 2009 Tundra 5.7L and was used as a construction vehicle. Not even sure of a good place to start. Would have been nice to talk to who ever worked on the issues of this thing and tell them to stay in the tire department. Spent a lot of time looking for a few broken wires. Which I actually just think the Ecm is not working properly. I'm supposed to take this thing on a 1300 mile drive north. I asked how it's been driving. "I've had no issues since the new battery been put in. But would like the cigarette lighter to work and you might want a radio to head north.... never listen to a woman.

First discovered, bad battery, won't charge, many lights not working. Foglights disabled, cigarette lighter unplugged, no speed meter, few fuses blower, really dirty engine, air filter bad shape, multiple dash lights..... and countless blue sharpie marks on fuses and wiring. By watching videos I'm amazed at how this thing is designed and the pain,time,and trouble many poor souls spend working on this very bad design of an engineer who needs that title removed from his name.(The person who approved it. You need to be fired)
But most don't care about the people that fix things anymore and it shows big time.
Anyway... I have drove this truck 4 times just kinda test drives. So I'm going into town to fill it up and get ready to hit the road. I noticed right away... no speed meter.(time has passed since I last drove it.) Ooooh yeah...I'll fix it before I go. Not even 5 mile down the road and RPMS drop right out. My foot lightly on gas and no power. Weird "no problems, drove fine." Luckily my friend is just another mile up the road. So I coast to the side hit the hazards. Shut it off. Start it back up and drive to friends. Man this thing just went goofy on me. We have both looked at it many times. I been saying Ecm needs to be replaced. But I'm ignored and the time I have spent on this thing is all been free. Good thing I grabbed the jumper pack. It seemed to not do it again so I head to town fill it up and put some injector cleaner in with some Heet to remove the water in gas tank. I'm heading back and it dies again. I jump it and get it to friends place. Tell him it died again. What the battery meter say? Ooooh man... just above 9, that means the alternator is not working after being replaced last time I was here. FLM. Have no clue what can make it not work again but when you have broken wires and have not found them is the cause. Theses are the codes it is thrown up while at the auto store. P0456,P0550,PO974,P0980,P0986,P2759,P0335,P0552. NO tire kickers. Toyota Tech if possible. Advice on what's causing this nightmare is welcomed. The price of things to be done on this thing is insane. 800$ to replace the alternator....Naw I'm good Sir.

 

In my opinion, as an HVAC technician and an at home mechanic lol
Problem starts with the fact it’s a former construction vehicle so like you said not a great place to start. Who knows what type of abuse that truck has been put through.
As for the codes, I’d say it’s more than likely the PCM or TCM. It is possible your ECU is playing a part in this. so you could either replace the modules or as I’ve seen mentioned on the forums plenty of times. You can get software to reset your ECU, see if that works and just go from there. At least the codes point you in the right direction.
additionally I would most definitely do a maintenance on the truck. Get nice and thorough, so you have a good idea of where that truck sits.