I went from an old 4 into 1 header to my nwor and have been fairly unimpressed. I'd like to get my truck tuned a little better, re-gear, then switch to my downey header and see if there's a noticable difference.
As for stuff you can do, efi limits you. Like I said, check downey's website for the afm adjustment. Once you have everything capped off properly you should be fine. Did you say if you checked your timing? I've also heard of people's motorbikes sitting around for a while then having no power, then the owner cuts the pipe in half and finds a mouse nest inside
