Sorry if this has been discussed. I couldn't find anything and I don't know to search using a phone.

I have decided to run true duals and long tubes. I am going to run pacesetter headers with 3 inch hi flow since that's the collector size. Where should I reduce it before or after the xpipe? Is there a lot of diffenece between the torgue on 2.5 and 2.25? Will the 2.5 perform better on the top end? At the same time I am also doing a gear swap so I will pick up some low end either way.

I have decide on magnaflow mufflers but don't know between 14 and 18. I want it to have a nice rumble but not so loud that u can't hear inside the truck when pulling trailers.

This is an 2001 5.4.

 

I would get 3" to 2.5" collectors to mount on instead of getting 3" cats, rey to run everything exactly 1 size. 2.25" performs better low end, 2.5 is better high end. I would go with the 18" bodies for less interior noise. The headers and cats will be loud enough inside.