Header and exhaust installation help

[CountryBoyFit83]

I have a 2004 GMC Sierra 1500, 5.3L V8, 4x4 SLE. I bought it stock with 140K miles just a month ago. I had Pacesetter 4-1 long tube headers installed with true dual straight pipes with glasspacks that dump right at the rear axle. With my experience and some people I talked to who know exhaust systems, all said that with that combination It shouldn't be hard to hear me comin from a mile away. That being said, when i start it up, it sounds like stock headers with a flowmaster 40 series Y'd into it. Not to mention I've had no change in gas mileage nor horsepower. It still performs like a stock truck. Not sure what the problem is but I think it may be because the person who installed the exhaust and headers put the cats 6 inches in front of the glasspacks, which are all located at the back of the cab or a little past. This is what I think it may be, however, I'd like to get others opinions on this so any kind of help would be greatly appreciated.

[SirManny]

I would recommend tuning the truck to accommodate for those mods and as far as sound goes im not sure what sound you are going for but that truck should have a decent rumble to it

[desrtrat]

what size primary tubes, and collector. too big is not always best..i would start by putting in a X pipe close to the collectors as possible. most will put it just behind the trans x member. get it tuned for the headers, and O2s ..louder, shorter glass packs, need to relocate the cats back where they belong, and hook up the o2's wiring properly, last..shoot the a-hole who did the hack job on the system..