When timing the Vortec 4.3 5.0 5.7 etc. I have read many peoples opinions saying this timing is not adjustable. Why is it that there is a circuit comparitor between the cam and crank sensors. This I was told has to be 0 the give the computer its base to be able to control timing. On my 96 the distributor is adjustable because it has an elongated slot cut in the holder. Can anyone clarify this situation because right now my truck is set at 0 degrees cam retard. Thks