I ran my truck down to the red empty mark, and beyond, this weekend (i didn't mean to) going over the Grapevine to L.A. pulling my RV. Went about another 15 miles after the empty light came on and the stupid overhead computer said that I had zero miles to empty. I finally made it to a truck stop and filled the tank with 34 gallons of fuel. If the tank really holds 38 gallons of fuel, I still had 4 gallons of fuel left. I was only getting about 10 M/G pulling my 10,000 lb. RV over a 4,000 ft mountian with a 6% grade going 70 MPH. Guess that I should go slower next time, but it sure was fun passing everyone up pulling my RV going up the mountain. These PSD are real pullers.