I have two f350 4x4 powerstrokes. One is a 4/96 build date and one is a 9/96 build date. The valve cover on the 4/96 shows 215hp and the valve cover on the 9/96 shows a 225hp rating. Does anyone know the exact difference? Is it the IDM or something with the hpop or the injectors? Both trucks are regular cab automatics.