fuel warning light

both on my k1500 2000 z71 i use to own, and on my now 04 gmc sierra 4x4 extended cab with 26 gallon tanks, most of the time when it came on, it would take 21-23 gallons to fill up, BUT i assume each truck is different. on my 04, i have the range meter and right before it goes to low fuel, it says i have about 40 miles left, and the gallon used meter says, 23, BUT again every truck is different depending on way you drive, best bet is when it comes on, start looking for fuel hope this helps

The few times I've let my 32 gal. tank get that low it always had 4 gallons left. You don't want to be out in the middle of nowhere!