actually I am betting he has a tier 2, 2004 with an 4g63 or 4g64, (the dash lights not going out right away is the clue), but the serial number sure would be a help.
Since I think this is an impco teir 2, I would also suggest that he disconnect the negative battery cable for about a 1/2 hour, and try it again. I am also wonderin how high the high idle is, as this trucks idle correctly at about 700 RPM but will run with the throttle body disconnected at about 500 rpm.
He may only have a stored major code, that will be cleared via a battery disconnect on this unit.
OR (my better guess) he may have an accelerator pedal sensor mal-adjustment or bad accelerator pot.