Yes stock 5.3L exhaust is SI/SO, 2.75". I believe the dual in of the SS muffler is also 2.75", so the Magnaflow Y can have 2.5" duals or you can get the one with 3" dual. The muffler shop I used just expanded the 2.5" duals and slipped the 2.75" SS dual pipes into the Y. The tailpipe on the SS exhaust it 3.5", it has two pipes coming out of the muffler which are both 3". Only one pipe is actually an outlet pipe for the exhaust, the other is an inlet to a resonation chamber to keep interior noise down. Not sure my GM put on a 3.5" tailpipe, the could have left it 3" all the way out since the outlet on the muffler is 3". When I had the SS muffler installed, the muffler shop left about 12" of the two inlet pipes on the SS muffler, hooked up the Magnaflow Y and used about 12" of the stock inlet pipe of the stock exhaust. It shouldn't be a problem.
Jim

 

thanks man! you've been very imformative!

 

btw the seller also said Stainless is this true?>

 

 

Yes, most OEM systems now are a lower grade of stainless to prevent corrosion from the water that drips pit of the tailpipe, it's corrosive.
In the last pic of the SS exhaust you can see where the two front pipes come together and are fairly even with one another, that's where my exhaust guys cut the pipes and installed the Magnaflow Y pipe. Glad I could help!
Jim

 

Cool thanks

 

This muffler shop I used (never again) was a real winner. When I took my SS muffler to be installed on my 03 he blabbed on how it was the same muffler I had with 2 pipes going in. Then he went on to say "Why don't we just cut off the tip, weld it on yours and you would have the same thing". GeeeeSH!
I said no please. He dropped my muffler and then took measurments against the SS unit to see if the hangars would work the same. The SS muffler was about 2 inches larger in all directions. I commented, "Same thing Huh?". He acted like he did not hear me. The hangars worked fine.

 

jackass

 

Y2K Silverado and others thanks for the help i got the ypipe that u suggested yestersday and in a few months it will go on thanks!