I noticed that it does depend on how hard you push on the accelerator as the truck can feel a little slow off the dime with a light foot. Recently I was merging on a freeway in traffic and pushed on the accelerator more than I usually do - the truck sure felt a lot peppier, I was surprised.
With that type of response, I wonder if you really need something like this with the 7.3L engine - if you want to save gas just feather the accelerator.