Of course its the ecu, and i think the only thing to do at this time, and everyone else is going to say the same thing, is check your wiring again, and again, and again, until you figure out your problem. I think thats the scariest part of a swap, first time or 100th time. See if you can try to change your rev limiter, but that might be the case because of the other codes, it might be limiting itself to 3k so the engine does not sustain any damage, which is protecting itself. Hey, just my 2 cents.