The AFC's function is to control pre-boost fueling (smoke). There is a pressure line to it from somewhere in the intake circuit (after the turbo) that allows it to move the AFC arm out of the way so that full fuel can be achieved, once boost has occured. If there is a malfunction in the system, the arm won't move enough to allow full fuel. You could have a blown diaphram, broken boost line, or other problem. Loosening the starwheel adjusts the amount of boost pressure needed to move the AFC arm, but if you have another problem the arm still won't move.
Thats why you should take it right off and run the truck. If you get smoke, you know the problem is in the AFC. If you don't, then the problem is elsewhere. You'll know the first time you hit the pedal.
Couple other thing's, slide the AFC full forward, and check to be sure that the shutdown arm is fully lifting, and not binding.