85 tpi iroc. Gutted cat,3 in in/out, all mandrel bend pipes from G.M. With stock crossflow, pulls better than before gutted cat, sounds much better too. Now, will aftermarket crossflow (flowmaster, dyno-max,etc ) REALLY make much difference, or by simply gutting cat, did I gain what i might have gained with aftermarket muffler?. With gutted cat, do i stand to gain a worth-while amount more with aftermarket? Appreciate your input. Thanks ahead of time.