The problem is not the gas tank, but your fuel guage. It reads a little too low when you might have 1/3 of a tank left. There is a TSB, but I don't think they will do it for free.
It was fixed in later models, my 2001 when the gas light comes on it has used around 16.5 gallons or about a two gallon resevre, with you being on empty it means you have 3.5 to 4 gallons left.
I guess the last owner learned to live with it.
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2001 & 2004 Toyota 4Runner SR5 4X2
Both V6 and both Natural White
"Yeah, I like white and I like 4Runners"