Just another note...when I brought the truck to the shop it was at -8. When they adjusted the distributor -6 was as close to spec as it would go. I was at the shop a few months back for the same issue and the timing as -13 and after adjusting -6 was as close to spec as it would get. I've watched a video on YouTube where a 5.7 vortec was -13 and rotated to 0 without moving the distributor one tooth. I don't understand why my truck's timing won't get any closer than -6. Is it possible that it's a camshaft position sensor or a crankshaft position sensor? It should be able to go from -13 to 0 with a very slight rotation of the distributor. Any ideas? Thx.