my 2007 f350 4x4 with a 5.4 gas motor with 200,000 kms. has a misfire on cold start ups and then about 1-2 minutes later slowly smooths out and then runs great.I can drive it and then shut it off and start back up and it runs great.only misfires on cold start ups. I have had it checked out done some work to it.seems to keep coming up as misfire on #8 cylinder.only trips the check engine light sometimes not always.some cold start ups misfire more violently than others.had 8 new plugs,move coil around & misfire did not follow.put new coil in, checked all elect. connectors, changed boot between coil and plug and I not sure what else the mechanic shop did but they seem to cover everything obvious things and it still misfires on cold starts.had them do a little more research and they think possibly could be a problem with cam phaser.not sure what this does but know it has something to do with the timing chain for that cam.they told me I would have to take it to a dealership since this takes special tools.could someone here tell me about cam phasers on these engines and if this could be the problem with my engine?and if you have any other suggestions I would love to get this problem fixed.its a great truck otherwise.Thanks !