Hi, I have a 97 E-150 5.4, 83,000miles that codes 171, and 174. I have crawled the whole engine looking for vacuum leaks, none found, even the expensive elbow at the back of the intake. I checked the fuel pressure, 30psi idle, 40 psi vacuum hose off, checked the EGR valve ( valve works good.), Checked the egr vacuum regulator (40 ohms) and cleaned all the inlet filters. The van pings under light acceleration at freeway speeds, reguardless of gas quality, and almost dies on initial cold startup. What am I missing?

thanks