6.0 exhaust

[rjd_j]

ok heres one for you lets see ho good you all are. i have a 2003 gmc 1500hd with the 6.0. i managed to destroy my first cat on my drivers side "intermidiate" pipe due to SOME OFFROADING so heres the thing, as far as i have reasearched this is a factory only pipe, which seems to me like it is a very expencive one due to the fact that it has two cats and two oxygen sensors. is ther any aftermarket product. if not.... i am a very skilled welder and if i removed the entire system.... instaled two high flow cats and two mufflers.... lets say 3" all the way..... and if i welded two bungs on each side... on in front and one in back of each cat... would this work? i smashd the stoc front left cat in.... and damaged the pipe where it bolts to the manifold. i repaired the stock pipe as best i could, but i sil have a small leak at the manifold. i also replaced a broken off oxygen sensor. i also removed the damaged cat so i could drive the truck and replaced it with a flexpipe. the truck will not shift correctly and at high rpm's skipps. is this due to the uneaqual resistances ion the pipes. if so will my idea of an exhaust system work? I used a scan tool and got two codes for the broken oxygen sensor that i replaced, and an engine misfire code and a mass airfol out of range code. i think the reason it is missfiring is because of the different resistances in the two intermidiate pipes. sory for the long post.

PLEASE HELP ME!