I have a 2000 chevy c2500 obs 5.7liter. I've been running lean for a while and I don't know how to fix it. I've replaced all o2 sensors, fuel pump, fuel pressure regulator, throttle position sensor, mass air flow sensor, and still running lean. Vacuum? It's possible but I did a compression check on each cylinder which all gave me about 180psi. Any ideas? Thanks.