You have the same setup is what I have now? How long have you had the GT500 mufflers? Did they get deeper over time?
I've had them since summer 2013. I installed the headers in December of that year then changed to the catted mid pipe in March.
The only time I noticed a change in muffler tone was when I installed the headers or changed the mid pipe. I actually did not like the GT500s behind the factory exhaust. I thought they sounded too blatty. The off-road pipe just made it too loud. The catted pipe took the edge off but they still get plenty loud when I open it up.