I've got a 2005 F350 diesel long bed with a 38 gallon fuel tank and 37,000 miles.
Yesterday I encountered a situation where the engine started acting like it was running out of fuel. I was pulling my 13,000 pound 5th wheel trailer over highway US-70 between Roswell and Alamogordo, New Mexico, starting the day in Caynon, Texas. I frquently will drive until the low fuel light comes on, whereupon I will fill the tank full with 30 to 31 gallons of diesel. So a couple of miles after I cross over the top of the pass the Low Fuel light comes one. I think to myself, fine, I've got 7 - 8 gallons left, 35 miles to my destination with a elevation drop of 3000 feet. No problem. I usually get 10mpg pulling the trailer on flat ground. Coasting down the pass could be better than 20.
I get to 15 miles from my destination, within 200 yards of the bottom of the pass, and the engine starts to act like its out of fuel. I ignore it for 30 seconds and then it does it again. So I start to be real concerned, find the closest parking place, drop off the trailer, and drive 1 mile back to buy some diesel. Turns out, I could only put 33 gallons in the tank.
So what was happening here? Was I really just about out of fuel? Or was the fuel pump sucking air because I was going down hill? Most of the pass was about a 5 to 6 per cent grade but the last 2 - 3 miles was probably a 2% grade. Is the tank not really 38 gallons? The most I've ever put in was 32.5 gallons. I suspect that driving down hill was the problem and that if I just continued on to my destination, I would have made it no problem.