My ‘03 Hemi quad cab Thunderroad had only the 26 gallon tank. While an average size for a 1500, that first year 5.7 Hemi drank like nobody’s business. Averaged 11-12mpg combined. Straight highway pulling my drag car/trailer @5500lbs it did average up to 16mpg. Just average stop and go killed range. Always at the pump with that truck.
Mine was a 2500 standard cab longbed with the same motor. She was a thirsty old girl. I got 13 combined in the winter, 14 in the summer, but I had the standard tranny and that's usually good for a couple of mpg. I'm pretty sure that I couldn't beat the 10-speed in normal mode today, it seems too well tuned for mileage. How many computers and how much software and how much expensive hardware does it take to beat a country boy using hundred-year-old tech? LOL