fuel gauge

2005 Tahoe Z71 5.3L 182,000 miles The manual says fuel capacity is 26 gallons. When I run it waaay down into the E on the gauge all it will accept is (today or any day previous) 15.7 gallons. Is the manual mistaken or is there some sort of obstruction that doesn't allow a complete fill...

I have a 2008 Tahoe and the situation (4 times now) is that my while driving, my Tahoe makes a sort of clunking sound and eventually stalls. The needle on the fuel tank indicator is at the last tick mark on the gauge, the computer shows I have about 100 miles remaining and the low fuel...