i wanted the most quiet muffler, 1 in 1 out is fine and the 12589 has those dimensions

 

IMO, I have there Cat Back kit and it seems pretty Quiet to me. It uses the same Dual in, Single out as the Denali kit

 

maybe its because im running catless longtube headers, i wanted it as quiet as stock

 

With LT's and no Cats it is going to be damn near impossible to get it as quiet as stock, even with a stock muffler it is going to be louder.

 

magnaflow 5x11x22 will be quietest and best you can get. you will like it. good luck with your project, rob.

 

Get the longest Magnaflow possible. I had a Yukon XL that I built for my wife and they are easy to get a terrible drone. What works, sounds good, and no drone on a truck will be too loud and drone like crazy on a SUV. I rain a 22" body on Stacey's truck but it had stock manifolds and cats on a 5.3. If you run the 22" oval muffler you might still have to run a glasspack to cut down the drone. I would say save up for a Corsa but people on here with a Corsa and castles exhaust say it's terrible. I had a Corsa on my Duramax with no cat and bigger downpipe and it was perfect. But a diesel is a little different.

 

i run 6.0, long tubes, no cats, magnaflow 22 3.5 and no drone whatsoever.

 

On a truck or SUV? I am assuming a truck since that's what is in your avatar. If you read my post I said what works on a truck doesn't work the same on a SUV. I had a 16" long Magnaflow on a crew cab 1500, I took the cats off and it was too loud. So I swapped it out and put it on my wife's Yukon. It sounded great, but the drone was so loud we could barely stand it. On a truck the exhaust gets trapped under a bed which as you know isn't apart of the passenger compartment. On a SUV it gets trapped under the rear of the truck which IS apart of the passenger compartment. I have Kooks LTs, hi flo cats and an 18" long Magnaflow on my TBSS now. It has some drone but if it didn't have cats it would obviously be much worse.

 

The exhaust on my TBSS is dumped before the axle and the truck is lowered on coil over almost tucking 265/40/22s. So it is a prime candidate to have drone, but the cats help keep it down.

 

i have not noticed any drone yet, knock on wood... mine is also dumped before the axle
here is a inside video.
04 Yukon Denali 6.0L SS Longtubes 22inch magnaflow dumped no cats - YouTube