I am doing true duals on mine and I am only going 2.25" pipe with same size Flowmaster 40's then just dumping it at the axle (cheaper than going over). Read the "Deals!" thread for Yankees expaination on back pressure... very good post!

Hey, i got a 2002 6.0L i got headers, two high flow cats, x-pipe, two 40 series flowmasters with 3" tubing the whole way, i only lose gas mileage cause i love the sound of my truck and got a heavy right foot. I don't ever throw check engine lights or have stalling or idle problems with my exhaust, if the exhaust place is telling you that then they are most likely a bunch of clowns, true duals is the only way to go!

If you plan on throwing turbos in at a later date go with the 3 inch. If not I'd back off a little. If you don't have enough back pressure you'll sound pretty loud, but will have some pretty bad lag on take off. Don't get me wrong, you'll get the speed eventually but it'll take longer than if you went with say a 2.5 or 2 inch all the way back.

6.0L is a lot bigger than the 5.3.... Maybe you can get away with true duals on your 6, but it's very unnecessary on the 5.3 unless you run boost.

I wouldn't go with true duals either. Your motor is not pushing enough power. Why not get a cutout? I have two mufflers that I can inter change on my 06' SS, and there is a BIG difference from the Flowmaster super 44 with the cutout, and my Corsa sport. I've proven it at the track too. I lost 2 tenths and 2 mph when having the duals with the flow. The duals sound mean, but so would a cutout when open.

Hi. I have a question on the same topic. I don't have a silverado though. Mine is an 81 scottsdale. I'm putting in a 350 bored .030 with a mild cam and a 625cfm Carter AFB performer carb and Edelbrock performer manifold and headers. For exhaust.... I had planned duals with 2 1/2 pipes to 2 1/2 cats (in and out) to a x-pipe to 2 1/2 in mufflers with 2 1/4 out to 2 1/4 tailpipes. Do you think this will work for my setup?
Thanks

3" is too big for your setup. If you dropped to 2" pipe, you'd see better performance.

You can run dual exhaust on anything, the pipe just has to be the right size.

I agree 100%