I'm trying to follow your math on the gas mileage. A total of 16 gallons was added to the tank. The truck was driven a total of 63 miles and idled for an hour. Since your sending unit doesn't work, at no time did you know how much gas was actually in the tank. How can you figure out your gas mileage given all of this?
When your filter goes dry, you likely have a fuel delivery problem which is likely caused by debris in the bottom of the tank. If the chunks are large enough, they won't even make it out of the tank to be caught by the filter. The fact that your fuel starvation symptoms are intermittent also indicates fuel tank debris. The chunks move around from the gas sloshing around when you drive it or when you add fuel. I had this problem before. The truck would idle all day long, but if you increased the demand on fuel consumption (driving) it would stall like it was out of gas. At idle, enough gas was getting past the crud to allow the engine to run.
