According to Fuelly(
LINK), new 1500s do get better fuel economy than the older ones in the real world. I am not sure if it is the case here, but for those only going by the computer mileage, many older vehicles were less accurate than newer ones.
Case in point is my father with his 2003 7.3L F350 and my brother's 2012 6.7L F350. My father used to think he got beter fuel economy than my brother because his truck's computer always shown 17-18 mpg while my brother's is around 15-16 mpg. After finally doing hand calculated numbers consistently, my father found out that his truck actually got worse fuel economy and that his computer was far less accurate than my brother's.
The same thing happened when I compared computer and hand calculated numbers from a friend's 2001 CTD 3500 to my 2014 CTD 2500. His computer shown that he got better fuel economy while my hand calculations proved otherwise.
