There are only 2 differences that set the Harley Davidson drivetrain apart from the Lightning. First, and most importantly, the Harley truck features a larger upper blower pulley which accounts for about a 2 psi LOSS in boost against the stock Lightning level. Secondly, the computer is programmed with a richer, and therefore "safer" air/fuel ratio and tune due to the utility nature of the Harley truck. Ford knows that most Harley owners are much more likely to haul loads or tow with these vehicles, so they tuned the computer with a safer air/fuel ratio than that of the lean 13:1 that the Lightning comes with. This really doesn't have much effect on horsepower, it is just mostly for safety, as the boost is the main performance difference.