OK, feeling like a nimrod here. I was going to post a link to the part I was talking about. But, to save SOME humiliation

It is the center section of the floor pan (if you were to divide a full0-side floor pan in three, this section is directly under the seat riser).
Thank you for time and experience.
George
BTW, I'm assuming your dually is a diesel seeing the power curve on your dyno chart !! The best I was able to dyno (before I detuned) was 425 rwhp / 899 ftlbs at the real wheels.....

__________________
1965 289 3 spd Rustang
2001 Dodge Cummins Dually
quote from the Greek
"I haven't had my engine on a dyno, but it's probably around 300HP at the crank or maybe a little more. I don't really know for sure, but if it was World War II, you could say that I've sunk the Japanese Fleet in my neighborhood. Remember Pearl Harbor!"