2006 Chevy Silverado Muffler

My question is about the muffler on my truck. I recently crawled underneath it, and from what I could see it was a dual in dual out 3 inch pipe. One, I would like to know my guestimate on the pipe size is correct, two if it is correct (or not) what would be a good muffler to put on my truck to give it a deeper louder tone, and three does it have to be a dual in dual out, because finding one with three inch pipe has been a bear! Haha. The closest muffler I have found has been a dual in/out flowmaster, the inlet is 3 inch and the outlet is 2.5, will this work? Any way, just need some correct answers to make further decisions, thanks!