[Bigglen]

Check out this custom made "true" cat back system on my 05 tundra 4.7
it uses a Flowmaster series 50 SUV muffler with custom made/bent tubes from the cats to the "Y" pipe. The "Y" pipe is a magnaflow 2.5 inch dual inlet to a 3 inch single outlet into the muffler, but retains the stock tailpipe so there is some backpressure. whole deal is about $250 installed.
I say "true" cat back system because all most all production aftermarket systems are "resonator" back systems, that is, they retain the stock resonator and "Y" pipe.