One last test for the exhaust leaks is to shove a leaf blower/shop vacu up the tail pipe and use windex at the manifold connections, if there leaks there will be bubbles. Do it cold of course. With an 03 a cheap mechanical pressure gauge can be installed in the oil cooler port on the filter housing. Get an aluminum plug the same thread size at the auto parts store and drilll and tap for the fitting.

 

If the ticking begins at start up and not when the engine temps get to 100 degrees or so then there may be hope it's not a slipped sleeve.

 

I've had several V8's that have had a worrisome ticking. So far, each time tightening the exhaust manifold bolts cured it, without needing new gaskets.