Engine suddenly started skipping overnight with no apparent cause. Mechanic runs a scan to reveal timing out by 27 degrees. Checks distributor and finds nothing wrong, says must be timing chain. Now says nothing wrong with timing chain. He is lost, doesn't know what to do even after consulting with GM mechanic friends. HELP!! By the way, just relaying to you what he told me. Know the mechanic very well and has been great in the past.