I had a very similar problem with my 2013 Rock Warrior (5.7). Long story short, it wound up being the fuel pump control module that is mounted on the left inner frame adjacent to the rear wheel.
There is only one nut holding this in place and it is easy to get to...
Well, what a horrible place to mount this unit, as it is very susceptible to water and road salt penetration. This controls the voltage going to the fuel pump and the part number is: 89571-34070.
Although technically a sealed unit, I pried my old one apart and the water and road salt had reached the inside. It was a mess.
I now carry an extra one or two with me. I have seen these on Ebay for as low as $25.00. The dealer retail is around $375.00.
I actually purchased two used ones that fit fit the 2013-2020 Lexus GS-350 (same part number) as these must be mounted in an area that is not susceptible to the elements, as they look brand new! I would not buy a used one for a Tundra, as these are all exposed o the elements.
There are a bunch of these new units on Ebay right now. I elected to go used, as I thought that these would be actually genuine Toyota original equipment. Some of these on Ebay may be from China... Who knows... I can not speak to the quality/
Here is one that I recently purchased on Ebay: 2013-2020 LEXUS GS350 FUEL PUMP CONTROL MODULE 89571-34070 OEM 13-20
- $US 25.00
Here a few photos to show you what these look like. The 2nd photo shows the Tundra bracket. If you look immediately above the rear left wheel/tire and look at the frame, you will see the nut. The module is immediately on the back side of the frame.