Here is what I have:
3.0 V6
Downey Headers
Hi-Flow Cat (model unknown)
Magnaflow muffler
2.5" exhaust from headers all the way to the back
Hi-Flow intake, K&N filter

Am I right in understanding that 90% of the exhaust noise is dictated by the muffler? I'd like to experiment, but don't want to spend a bunch of money. What about those Summit Turbo mufflers? Quieter? Maybe just try and fit the longest muffler I can underneath?

Would more backpressure give more torque? Engine runs strong at higher RPM's, but seems to have next to nothing when crawling. I would not ming loosing some upper end HP if I got more low end torque... and I sure wouldn't mind dropping the noise level a bit.

Suggestions? Ideas?

 

The 2.5" catback is killing your torque. I made that same mistake when setting up my exhuast. 2" or 2 1/4" is what you need for your muff and tailpipe. This will restore all of your low end torque.

I am running downey headers, a highflow 2.5" cat, and a 2" dynomax super turbo cat back ($95 from summit ). It is quiet, and you'll be surprised with the power increase. 2.5" is simply too big for the 3.0.

 

run 2-1/4" pipe from the cat back if you want it queit go with a 24'' magnaflow muffler

 

2.25" is definately the way to go for torque. As for noise a lot of it is the muffler, and there are mufflers that are designed to be quieter. The downside to a quieter muffler is that it has more baffles, and tends to introduce even more back pressure to the exhaust system.