Many-many thanks for posting this.
I have an 08'LGT and have recently gone to a Cobb stage 2 tune with a more free flowing air-filter and colder plugs( other supporting mods for the tune). I was out the other night and experienced the noted rough idle. I cursed the mods and thought about all the things it could be. It was also -5 out (if you haven't guessed, I live in Chicago).
I'll be getting some gaskets this weekend and thanks for the 'how to' above.
Power to BMX045( I grew up in Arlington MA- word to Btown)