If you do like three6gmc said, and find a good used 6.2L factory exhaust, youll be getting a 3.5" catback that flows good and you can "grow" into it. you could come out cheaper than buying a new 3" catback. It all depends on how long u plan to keep the truck and how mild/wild you wana get with it.

 

I'd just put a 4" muffler (no blowmatser though) on it and keep the stock pipe size. Your restrictions in your cats and mufflers. Make sure they terminate the exhaust pipe about 15% inside your muffler, and use good reducers to exit to your tail pipe. This will keep restriction to a minimum but also keep the exhaust velocity up where it needs to be for good exhaust evacuation.

 

I'm with others on here. Find a 6.2 system. they are proven to flow extremely well and the average muffler shop can't even build a system as effective.

 

Yup, and they even sound pretty damn good imho.

 

I love the way mine sounds on cold startup. The only thing I have considered is removing the resonator in the back but I doubt there would be any gain to a stock 6.2 so I will leave it alone.

 

I have a corsa touring cat back on my 09 6.2 Sierra Denali. Just as quiet as stock cruising on highway no drone and deep throaty sound getting on the gas.

 

So does the 6.2 exhaust flow good / will I see HP gains if I put a magnaflow muffler on it? I guess all I need to do is buy a 6.2 catback setup, and weld a magna flow muffler onto it, yeah? Do I need to have any resonators cut off?

 

Yes it flows good. Good enough to allow a 6.2L to make 400hp stock so I would assume it would be more than enough for a 5.3L.

 

Werd!!!

 

Here's a Stainless Works true dual 2.5" catback system on trailblazer with 5.3. For more sound you could tap into factory exhaust after cats and use the Stainless Works performance connection setup for true duals from manifolds back. This would not affect emissions nor require a retune.

Chevrolet Trailblazer 5.3 V8 Stainless Works true dual exhaust TBSSTD-LMF-CB- Done Part 2 - YouTube

Below is a custom true dual from factory cats to exhaust tips, very nice look and good sound. The Stainless Works mufflers flow better than the single Pro-Flo with dual in/dual out. I spoke with Pro-Flo to get their cfm numbers and their 3.5" single in/out flows more than the dual in/out pictured.

2011 GMC Denali 1500 6.2 Custom True Dual with Flo~Pro muffler by Kinney's. - YouTube