Thank you for the comment on my exhaust, much appreciated
To contribute, everyone is on the ball about the 14". With stock converters and a muffler swap only mating to a single tailpipe the 14" will be better heard and the sound will be megaphoned perfectly with a 4x12" tip.
The stock exhaust in these trucks are stainless but natural finished stainless. The stock tailpipes on 2004+ trucks are 2.75", with the rest being 2.5".
The muffler part # I would suggest to you is
11226, its the 4x9 oval 14" SI/SO 2.5" The offset end will be the inlet and centered end will be the outlet and should line up perfect.
You could use the OEM tailpipe but it wil need its ends flared down to fit but it would still work. Wish you luck on your search.