Hello all. I just inherited a 2003 Toyota Tundra and have started the repairs.

And to piggyback, "OEM" doesn't always mean "Toyota brand" or "bought at dealership". The thread you've been suggested to read explains in more details. For electronics it may be Denso or Hitachi, or for plugs Toyota may recommend Denso or NGK. For brakes, it's Advics brand. For a number of mechanical parts like water pump, timing belt, and a variety of other things it's Aisin brand. You'll pay less buying direct from those brands, or the brand names if you know them. But all the same 3x-4x longevity over anything else aftermarket for less money. But whatever you do, don't buy the cheapest part you can find, and don't buy generics/off-brand. You're asking for a world of hurt on these trucks.