I know this thread is a month old, but I am running into something similar on the 2004 Yukon I picked up 2 weeks ago.
I picked it up with roughly half a tank. Drove it a couple of days, and had a few other issues creep up (O2's, plugs). As I was diagnosing it in the garage, it was running pig rich and chewing through fuel. Anyway, by the time I got those items buttoned up, it was just above E, no gas light on....darn thing ran bone dry in my garage and wouldn't start.
I threw 2 gallons in it from my lawnmower can and took it up to the gas station...~18 gallons later, the auto shut off on the station pump tripped. I thought that was weird, being that's a 26 gallon tank, but also know those can trip early. Didn't want to push it and pour fuel down the side of it, so I left well enough alone.
Fast forward about a week - during this time, I ran the tank relatively low and threw in some good fuel injector cleaner, and have thrown a couple of gallons into the tank here and there - point is, from what I was tracking, I should have been close to consuming everything I topped off during this period and the 20 gallons I put in from my first fill up. I ASSumed I had 4-6 gallons of usable gas left in the tank, being that it's a 26 gallon tank. I planned on topping off the tank on the way into work this morning....
...except it wouldn't start at all. Filled up my 2 gallon tank again, dumped it in, and she fired right up. Went straight to the gas station 1 mile away and proceeded to put 18 gallons in it....for a total of 20. This time I really tried to push past the first "autostop" on the station pump, and no - it truly was full. The DIC was showing I still had 90+ miles on the tank. I also had no "low gas" light - I know it works, as I've seen it illuminate before I fire up the engine.
So, in summary - my 26 gallon tank seems to only allow me to use 20 gallons. When the truck is dead out of fuel, I can only add 20 gallons in. To me this isn't necessarily just a fuel sender issue. It's almost like the pump is pulling from too high in the tank and can't reach the last 6 gallons. The bummer, too, is that I can't rely on the range meter as the truck seems to be assuming I can get to that last 4-6 gallons when it actuality it runs dry.
