well afte trying to find the answer I came up with the problem. the 04 wrx has a different OBD II rear o2 signal than on the previous wrx's . which means in short, when you remove the rear cat, and attempt to compensate for this, getting rid of ithe P0420 code by using a CEL fix, you get a CEL P0139 (slow sensor speed).
Through trial and error I found this out. Pony express, and caspers don't have the answer yet and will not for a while, so I can 1 get the pcm re-flashed or 2 live with it for now. since I plan on further mods, I will sit on It for a minnute
hope this helps!