Keith I was having a fuel pressure discussion about the 3rd Gens and the thought is once you've maxed horsepower with injectors and a box, and assuming you have adequate fuel supply to the HP pump, then the limitation is now with the HP pump, line to the fuel rail or the fuel rail itself. With the high pressures required for operation and performance of this system, the demand is very very high to maintain that pressure while at the same time delivering the needed volume of fuel. When you reach the system's limitations pressure will drop and therefore you cannot gain any more HP. Just like the VP44 or anything else every injection pump has its limits.
Vaughn