The '08 3.0 got the tappets replaced and when it didn't fix the ticking noise it's got the cylinder head replaced. After this it's been having the rough start problem since then. For a few seconds after the start up, the car rocks along with the engine and the rpm needle moves fast even while stationary.

It has the symptoms of cylinder misfire. And it probably is. But the dealer claims it can't find a fault code stored. Let us know how it goes.