Turns out it was the timing chain. It had just enough slack in it to knock the timing out the same degree each time...negative 45. Sometimes the last resort should be the first!

We have had a 1996 Chevrolet C1500 in our shop for a week. We have tried to set the timing with a Snapon Modis Scanner and it shows -45 degrees. Replaced Distributor, PCM, checked the camshaft gear (teeth), checked the timing chain, double checked the TPS sensor, and followed the MODIS scanner proce...