The first symptom was my 2004 Tahoe would not start after it had set for 6+ hours, the only way to start it was to hold the gas pedal to the floor which causes a massive amount of black smoke out of the exhaust. The dealer happen to see a code that he said was a fuel error. He interpreted it to mean that the vehicle thought it had E85 fuel when in reality it did not. The dealer has replace the computer system, fuel sensors, check fuel pressure regulator and replaced one air flow sensor without any luck. I took it upon myself to test his theory so I filled it with E85 and the vehicle runs like a champ! However once I put any standard unleaded fuel in it it goes back to it's old ways. Anybody got any ideas.