So your A2 has the DDEC IV electronics? Is there a screen for it in the cab or do you have to plug it in to a computer? I think I'd dial it down if it were mine, or at least check... Maybe it's jacked up sky high. We certainly don't need 500 hp running down the highway empty, and it might improve your fuel economy. The 2 mpg rating is for GCWR (100,000 lbs) on mixed terrain. I'm certainly hoping for marked improvement at 1/2 that weight cruising on the freeway.
Your truck also has the 6-speed trans? How do you like it? Have you driven a 4-speed to compare? I assume the transmission is electronic too, and interfaces with the DDEC computer? It has crossed my mind that if anything happens to the 4-speed in my truck, I'd put in a 6-speed. But being electronic vs. mechanical, I don't know if it would work.
Jon