I got rid of my american thunder system PN 17233. It sounded good at low rpm but sounded crappy over 3500 rpm. It sounded like a dump truck. I put on the Hooker 3" catback with the aero muffler the other day and it sounds awesome. Everyone I've seen says its 10X better and that it sounds the way a muscle car should. I let my brother drive the car so I could listen and I agree 100%.
When I had my original 305 in the car I replaced just the stock muffer with the flowmaster and it sounded good so thats why I bought the complete american thunder for the 350 and header install. It just never sounded as good though for some reason... maybe its just that kit. My brother also has just the flowmaster muffler on his 5.7 IROC with a procharger and it sounds great so I just don't get it.
Anyway just thought I'd share my opinion and experience.
later.

 

I just wanted to add that I took the Hooker tips off for a short time and drove it and it didn't sound nearly as good. I think the sound was bouncing off or was being absorbed by the inside of the rear bumper. I think the tips are the key to this system sounding good as it extends your tailpipes past the bumper by a 1/2 inch or so.