Truck Forums - 2004 Sierra 5.3L Exhaust Questions

I'm currently in Altus OK and am looking for good places in either OKC or Dallas area for the vehicle work.

I have a 2004 Sierra(125k) with a K&N FIPK Intake and a Flowmaster 1 into 2 muffler with dual pipes straight out the back. Recently the right catalytic converter has started rattling HORRIBLY. I've heard I should replace both cats because if one is bad the other is probably close behind it. Ive also heard that I should just get rid of them and then custom tune the truck for optimal performance, and to make sure I dont get a check engine light by removing the cats. Then I read on here that the 5.3L doesn't like to be opened up because of the lack of back pressure. I also worry that going catless will change the sound of the exhaust to a sloppy loud sound instead of what I currently have and like with the current stock cats and Flowmaster muffler. Any ideas/recommendations?

As far as tuning the vehicle I talked with a guy at PCMforless.com and he seemed really knowledgeable about my vehicle. However, after browsing this site I'm wondering if I should email them my info for a one time PCM reprogram, take the truck to a shop where it can be dyno'd and tuned, or if I should get the computer/software to do it myself. I've heard that tunes can change everything from Speedo deviation, transmission shiftpoints, engine fuel/air mixture, remove the GMC traction control, etc. I've heard that it optimizes the performance to get more horsepower and better gas mileage. Im not planning on doing any more upgrades to the truck after its tuned. Is this something I should tackle myself or just have done for me? Once again Ideas/Recommendations?

One last thought is I'm wondering about the underdriven pulley set? Worth the hassle?

Thanks...