I have an Excursion and duals would be a pain. As is you have to relocate the shock to the outside so the tailpipe doesn't rub on it. The differance in stock to 4" is huge if you get a turbo back system. The factory down pipe leaves a lot to be desired. The use of a muffler isn't nesessary. Psd's don't drone inside under a load. We don't have salt on the roads up here so I bought a turbo back system from Summit Racing for $299.00 and the shipping charge was $8.00!!!!!