Quite a bit of discussion on this subject in the exhaust sticky in this sub-forum but IIRC Dan and Dave did a back to back muffler/exhaust comparison along with the intake manifold testing and as far as the stock appearing systems found Wilkinson's stainless exhaust are a significant improvement over the so-called "GTS System" in power and eliminating the ~2-2.5 krpm resonance.
I must admit, my mind is trained to seeing the stock cans on the rear end of a Pantera.
Best,
Kelly
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.