In all my years and all my miles driven, all my motors and all my motor head friends and all their motors I have heard stories of jumping timing chains. I have however never seen one or found a way to make it happen. Now the chains on the V6 are long, but if you look at a chain of any kind you will see that it just can??t ??slip?. In order for this to happen the cams would have to turn faster the crank and overcome the tensioner causing slack on the inbound side of the crank sprocket. This just would not happen since the cams have no way of going faster then the crank. Now, if the engine was rotated backwards a few times with no pressure on the tensioner I could see how you would get slack on the wrong side of the chain and possibly get it out of sync. This is why OHC engines should not be rotated opposite of normal rotation.
Ask your mechanic for a better explanation and do some more troubleshooting before you tare the heads off.
jeff
