I'm running MBRP. I ran a Magnaflow on my 04.5 initially and left it alone for 3 years before the drone started to annoy me. I ended up switching to an MBRP muffler. The MBRP muffler was 8" longer than the Magnaflow so right off the bat, my drone was gone. So, when I traded in, not knowing anything about the LBZ and how quiet it was, the natural thing for me to do was purchase an MBRP kit. Now, I couldn't be happier. I have a 4" and that's plenty. Don't waste your money on a 5" kit. Thats more for bragging rights. Some say that a 5" will be a deeper tone but you're not gonna gain anything with a 5" that a 4" wont do for you. The only difference is the price difference between the two.
The full 4" kit is in the $350 range, depending on who you get it from and what kind of deal they give to you. I'm a stickler about noise and don't like a lot of it. Thats why when I bought my kit, I bought a resonator (separate from the kit) and had it installed when they did my full kit. It's super tame and does not drone at all. In fact, at normal cruising speed, you'll never know you have an exhaust on there at all. These trucks have come a long ways over the years so they're really not loud at all. Your turbo will be loud as shit but most of us seem to like that part.
The bottom line is that all the exhaust systems do the same thing. They all get rid of the cat if you so choose and open it up to a 4" pipe from the turbo back. They all sound good. They all make the turbo loud. They all reduce EGT's and do produce more power. A cat back has been dyno proven to increase 11 h.p. over stock. The cat is relatively free flowing but the stock muffler was the real restriction, not the cat. So, 11 h.p. over stock is pretty decent with a cat back. Take the cat off and you'll get more. Most people had their mileage jump too simply because of the lack of restriction. It's gonna breathe better, just like an air intake or PPE air box mod. It inhales better so in turn it's gonna want to exhale better.
