whats all involved in the install? I take the stock y pipe would have to mod modified to work?

i just wanted to make sure they would work on a 04 5.3 4x4

 

According to their website and what I've learned here, the ASM's are 4x4 friendly. If using the stock y-pipe, it has to be cut and flanges are welded on to it...I believe the headers come with the flanges.

 

Not sure about 4x4 fitment, but the pipes are cut like 1/2" before the cats and supplied flanges welded on to them. I actually had to have the y-pipe cut snd have an offset welded in because of alignment issues. No biggie.
However, the one thing I wish I would have done differently was to look at going catless and getting O2 simulators. Since the shop had there hands right there, I dont think it would have cost anymore.

 

They are 4x4 friendly. I had to section my y-pipe for an alignment issue as well. I took about an inch out of the pipe under the engine.

 

they work just fine. and they are awesome.