Originally Posted by hog

Just to clarify some things. About 15 miuntes ago, I measured the exhaust on a 2006 Chev 6.0L 2500 truck with a Vernier Caliper. The truck was on the alignment rack to get its frame straightened

here are the findings:
From the factory the 3/4 ton exhaust exits the exhaust manifold into about two inches of 2.5" pipe that expands into dual 3"tubing, this goes into dual 3" cats, the cats exit into dual 3' tubing into a dual 3" inlet muffler with a single 3.5" outlet into a single 3.5" tailpipe.

I really wish I had a digital camera handy, I cant beleiev how big this dual 3' mandrel bent factory exhaust looks. Its a big improvement over my stock Vortec 350's dual 1 7/8" headpipes(pipes that connect the manifolds to the cats). My stock headpipes were crimp bent from the factory. On both headpipes there was bends that crimped the diameter down to under 1 1/2"'s.
Now these newer trucks are running dual 3" headpipes with mandrel bends, the exhaust diameter is practically double, but the engine only has 14 more cubic inches of engine dispalcement. if I put dual 3" headpipes on my truck, low rpm torque would suffer as well.

I ran my longtube headers open once and los a TON of low rpm torque, the truck wouldnt launch hard at all, but would scream above 4500rpm.

I am now running dual 2.5" headpipes and cats and wouldnt suggest to go any bigger than that on a 350 unless forced induction came into play.

A 2" h-pipe, connecting both banks of exhaust, placed before the cats would certainly help the low rpm torque. But it has been stated that an H-pipe is allready in use.
I have read that placing an H-pipe as clos eto the headers as possible that is 1/3 the diameter of the rest of the exhaust will bolster low/mid rpm torque WITHOUT sacrificing ANY high rpm power. This type of H-pipe allows the exhaust pulses to scavenge the exhaust charge out of the combustion chamber more than when dual exhaust has no H-pipe at all.

Getting a proper PCM tune by 1 of the many PCM tuners will help, that Superchips unit isnt what you need in this case. I would go to Nelsons in this case, or possibly Westers, they both have a nice 496 8.1L tune.

peace
Hog