I have a 2000 chevrolet camaro v6 auto with 127000 miles on. The engine has a high rpm and when I give it gas and then let off the accelerator the rpms goes slowly down and the engine growls as the rpms go down slowly, and the exhaust cackles as well. Thats in overdrive, if I have it in regular drive the passing gear it maddly acelerates but after it seems to not ever want to shift again and snarls exhaust cackles real bad. Its acting as though I have a manual and not shifting out of third and im near redline. It also in the morning or whenever I let it cool for longer for 10 mins and start it up the engine has a clicking noise near the exhaust manifold/headers and then the engine gets warms up it goes away and stays away until it sits again. I had lots of things checked out vaccum leaks, fuel systems need cleaning,o2 sensor changed, fuel filter changer full spark plug wires and checked had 2 coils replaced, it runs better. No engine light is on, nobody can figure it out. I had to fix the cataylic converter and full exhaust when I bought and it has hiflow cat with full flowmaster exhaust to the cat, people tell me since I had that changed its that. But it started it before you couldnt hear it in the exhaust as you can now, Im stumped I thought maybe its timing chain or stinking throttle linkage but I dont want to go spend more money unless I know for sure. Thanks for your help