Hi, I'm Earth. Have we met?
When my light comes on it usually takes about 28/29 gals to fill it up and its a 34 gal tank ( i think???). As some have learned the hard way the fuel gauge isnt always telling the truth in these trucks!! I know one guy whos truck would run out and the gauge said 1/4 tank all the time with no light, but this was on a dual tank dump truck so who knows ?