Keep in mind that your gauge may not read correctly too - I'm not sure about this.
I DO know that when I swapped my gauge cluster in my non-SR5 4Runner for the SR5 one, it changed; my guage now goes all the way to the botto, and stays there for another 1/4-ish of a tannk before the light comes on and it's actually empty. I'm guessing this is b/c it's calibrated for a smaller tank (I must have the 17 gal)

With 200+ Billion electrical parts, the world most complicated machine is inside your own skull.

Question Reality.
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'89 Rnr DLX "SR4.5", 32s w/ 5.29 locked f/r blah blah