Last weekend I did a LS1 swap in my 04 Avalanche, current setup is a single dual out Maganaflow which had a nice mellow note on my dearly departed LQ4. With the LS1 and shorty headers it almost as quiet as stock...so what am I looking for? A nice clean tone that sounds more like a Fbody/Corvette than a typical sport truck.

Engine details: Crate LS1 from SD with stock 0965 cam.

 

keep the muffler and swap those shorty headers for some tsp 1 7/8 headers with a nice ORY. that should give you more noise and power to boot.