I've seen in here, or somewhere, that the crank/timing belt sprocket can slip, or be broken from it's mount if not put on correctly (or just age). Then timing problems can result, and you can be out of time even when you set it according to the +5 mark.
It's in Viper's list above, he reset timing as part of the cure. Maybe you could pull the timing cover and belt, so you can remove that pulley and check. The cure was to drill and put pins into the crank and pulley. There were two people there, who had that problem and solution. They both did the drill/pin technique, maybe because the crank was also damaged, or because the pulley was costly.
One other thing, maybe your Cat.