One of the filters in my cat broke loose inside it wasn't from the T6 (which I do use), but the symptoms were pretty much the same thing for me as soon as I cut the cat off my power returned to normal.

 

My cat has always been a rattling rust trap. Perhaps it was coincidence the cat totally failed at the same time as my oil change?

 

It is possible that it is a coincidence, a new catalytic converter doesn't cost that much money but when mine failed I replaced the whole exhaust for about $360. I would probably get an opinion before cutting into it though.

 

Buy a vacuum gauge. Read the directions for testing the exhaust system.

 

yep.. that 5w or 10w stuff just wont cut it down here.. some people do not realize.. if its 5w 30 when its cold its got the viscosity of 30w.. once oil temp hits 200... it has the viscosity of 5 weight...now these import engines with their very tight clearances... that is a different animal all together .. you have to run CLOSE to what they recommend you use .. like if it says use 5w 30.. i would recommend 10w 40 down here..