3" may be a little big. i run a true dual 2.5" on my 5.2 yj and it flows everything it can plus some. your mufflers will tell the tale over the size of the pipe. i realize your running a single dump. there may be no detriment but i don't believe you will gain any performance from the 3", like i said my .02 is choose a quality performance muffler and keep the pipes at 2.5".
as hesser said... i had the headers, cat, and mufflers already in place, had the shop build me a set of tail pipes, and i walked away with less than a $200 bill to make tailpipes, hangars, and mounts.