My truck is in dire need of a tuneup, so I stopped at the local autoparts store tonight and got quotes for an Ac Delco tuneup. One thing puzzled us. The rotor had 2 listings, a D447 and a D470. One is special order only and for TBI, but it doesn't explain the difference between them, does anyone know? Plugs, wires, cap and rotor from AC Delco comes to $108. It hurts, but it needs it bad, last tuneup was Oct. 2010.