I have a 1999 2500 V10 no spark on plugs 8 or 9 (same coil) I have checked plugs, plug wires and coil by switching them with known good parts form other cylinders and a new $144 coil. I suspect the Powertrain control unit is bad. I have checked wireing and connectors and all seem good. Truck only has 69000 miles on it but still 10 years old. Is there any other known cause for just one coil out of the 5 not working?