Just got my new muffler in from fedex today and went by what I read and got 3" in 3" out (Hooker Aerochamber muffler), however the stock y pipe where the muffler should connect is clearly not 3" pipe and looks like it will require maybe a 2.75" to 3" connector?
For anybody that put just a muffler on what size did you get and did you need any reducer connectors?

 

Its a 2.5" on my truck after the cat. I have a 4.7L, not sure if its different amongst motors. My tailpipe piping is def 3" though.

 

I bought a magnaflow 3" in-3" out and it fit perfect on my Hemi.

 

I installed a flowmaster cat back system on my 05. Muffler was 3" in but came with an adapter. Everything fit perfectly

 

Giving up on your stock muffler? I'm runing a similar setup with a '09 muff hooked up to dual tailpies. Everything should be 3" on a HEMI. Let us know how it turns out!