Looking for some Exhaust assistance

A friend of mine sold me a pretty nice section of exhaust (from the muffler back, not including the muffler) and he gave me a good deal on it so I took it. I took my truck to the shop and was going to install it myself, but the stock exhaust is 2.25" (if I remember correctly) and the one I bought is 3". I was going to cut the stock exhaust right behind the muffler and clamp the aftermarket one on, but there is too much of a gap. My question is am I going to have to buy a new muffler or is there a way I can still install the one I bought. Also, will installing a 3" pipe after the muffler affect the performance or the sound? I'd like to prevent that if I can, obviously. Its a really nice SS pipe with a good tip so I'd like to take advantage of it. If needed I can post a picture or two of the SS pipe I have. Also, my truck is a 2013 OR 4X4

 

Depending on the OD and ID of the pipe you are working with, choose one of these:

http://www.summitracing.com/search/...d-reducers?N=4294898539+4294797469+4294808151