I just got done installing 15821 on my 05 f-150 which I purchased stage 1 custom tune kit Going troyer performance on wednesday morning to dyno and tune the truck for the kit. I called Magnaflow today before I installed the kit. I was a little worried because I'm reading on the box for 2004. They told me their extra pipe for the 2005. I was relieved. My little issue was why didn't they send about 24" straight extension pipe with the kit, which goes before the muffler. It can't be that more costly to throw in a 3"straight pipe. It would've made the install easier because it looks like band with 2 bolts hold the straight pipe on.