Lackey seems to have an elbow problem which the Red Sox were warned about by at least one doctor, according to the Globe, when they signed him.
I don't know what Zito's problem is. But in the steroid/big money era, there have been frequent spikes in performance in contract years followed by declines after the big contract has been procured.
Part of that may be conditioning, part of it mental. Players bust their tail in contract years, then slack off after they land the big fish. What was CCs problem with his slow start? Was it conditioning, or pressing?