have you done the pcv plate on the back of the intake? another possible problem is a plugged cat v8s are real bad on that, i've seen a small problem drive the fuel injection computer absolutly nuts on the v8 it's too quick to adapt to problems, i've seen a plugged cat on one side blow the pcv plate and that cause the computer to throw the mixture 50% lean on one bank and 50% rich on the other in 5 minutes of running after a complete reset of the computer
all america wants is cold beer warm cat and a place to take a poop with a door on it